You said it all right here. This is a real problem in talking about lighting, it's nearly all bull and noise, this thread is no exception unfortunately.
At the risk of provoking further noise here I'll share what I know on the topic and then probably get told I'm dumb and wrong and then we'll have even more noise to trudge through.
Optics are manufactured around a particular type of emitter. This means reflectors or lenses built for an incandescent filament are going to be out of focus if you put a different type of emitter (LED or HID) in there. Even if that emitter costs a lot of money and lots of dudebros on the internet swear it's like, brighter bro.
I think it bears consideration that the engineers who develop automotive headlamps probably have some qualifications to back up their career and if they want to build a reflector or lens arrangement around an LED emitter they will, but if it was built around a filament emitter it was probably built a specific way for a reason. Often for DOT/SAE/ECE constrained products that had to do with the state of the regulation at the time the product was manufactured - noting that those regulations have changed a few times over the years too. As I understand it the present DOT language is written around the brightness of a focal peak on incandescent reflectors and that will necessarily produce different results when the same language is applied to the brightness of a uniform field projector (regardless of emitter technology) that does not have a focal peak.
The engineers who develop aftermarket retrofits and such are surely qualified as well but their goal is to sell you a product "for off road use only" and it doesn't have to be good for it to meet their design objective .
A light which "looks brighter" when you stand outside your vehicle and look back at it is not the same thing as "reveals more information about the road ahead" . These are two different things. A really good lamp will look fairly dim from outside its focal area because.. uhh.. light's not supposed to just get spammed out everywhere. You want to see what's ahead in the road there's no value in lighting up the dust on your windshield and raindrops or fog 10 feet above your car. If you think about the projector at a drive-in movie theater, its job is to light up the screen not the whole parking lot so if you look at the projector from below its focal range it doesn't look all that bright.
Near field glare is bad for your night vision. Pupils constrict when a lot of light hits your retina, that's how normal eyes function. If you're utterly blasting out light everywhere and it's reflecting back at you from the pavement 15 feet in front of your car it's going to negatively affect how many photons can get into your eyeballs from objects 100 meters up the road. At highway speed you don't really need to know anything about the road 10 feet ahead of you because you already drove over that by the time your mind could process it. You need that distant information. This is why optics are as important if not more important than lumens. You need the right light in the right place and eyeballs don't work exactly like digital cameras work.
A word on color temperature and CRI - light comes in different wavelengths, just like sound does. You have to keep that in mind, and keep in mind the task you're actually trying to accomplish. If you're serving food to somebody you want high CRI lighting so the colors of the food pop and look natural right? Because we're super excited by bright fresh looking food.
But when you're driving a car it's less important for you to admire the coat of the deer you're about to hit and more important that you get clear information about where it is. You want your eyes sharp, not watery and fatigued from looking at glare for hours.
That's where blue light comes in. Blue light is simply not great in headlights because it focuses just slightly forward of your retina. That's why illuminated blue signs look a little bit blurry compared to similar illuminated red signs of the same size, intensity and distance from you. That's not a subjective property or an opinion. In the case of headlights this effect reduces the crispness of illuminated objects in the distance which may make it harder for you to pick out the edges of something and the lack of focus also increases fatigue which will affect your comfort and mood on long night drives. Rich blue light is simply not desirable on headlamps for driving. You don't need to filter it out but you sure don't want it emphasized.
It becomes worthwhile to remember that in the case of LED emitters the diode itself always emits just one wavelength. There is no such thing as a white LED at the emitter level - they're actually blue LEDs. The diode is built with a phosphor filter in front of it which absorbs some of the blue light and re-emits it at longer wavelengths, like green and yellow. White is every visible wavelength and a white LED is really a blue LED which combines with yellow and green to produce white. The distance between the blue emitter and its phosphor filter is why you often see bluish or yellowish bands at the edge of areas illuminated by a white LED. This all matters where we talk about color because white LEDs still contain a ton of blue light and blue light sucks in the context of headlights. Incandescent lamps naturally make very little blue. For what it's worth, xenon/HID bulbs typically have a few color peaks from the excited gases but the overall bandwidth of visible light can be very consistent.
For the above reasons I choose to use halogen lamps for most of my forward illumination. Cost is not a factor nor is any inferred kinship to Ned Ludd. I don't have an opposition to LED in the correct applications but we must exercise nuance here and not resign ourselves to caveman thinking like "LED GOOD HALOGEN BAD!", it's just not that simple. You have to consider the objective and the mechanism or you're just slapping junk together and getting junk results.
I use LEDs in handheld flashlights. There battery life is a major consideration, I don't walk at 70mph and generally don't find myself depending on their illumination for a whole day. I also use LEDs in some household lamp applications but again I'm not trying to send the light to a specific location (up the road hundreds of feet..) so distributing the lighting everywhere is a good thing, and the fashion of household lighting is more toward warm color temperatures so most household LEDs have large remote phosphors (the visible orange bits you can often see) that cut down the blue LED emissions a lot. It's an apples/potatoes comparison.
So to wrap this up with specifics on what I personally use for illumination; I use the factory lamp assemblies in both of my vehicles but take the time to aim them properly and I use Wagner Night Defense bulbs. They're a white halogen bulb with zoned yellowish filters. It seems like a gimmick but after using them a couple years I'm sold, the gimmick works and my eyes don't get sore on all nighters. For high beam driving aux lamps I use PIAA 520 SMR lamps which are a purely white halogen beam in a pattern that I believe is well suited to highway speeds. I have them tied to my vehicle's high beams so dipping to low beams cuts the driving lights, which is a matter of simple convenience and mercy for oncoming drivers if I see their approach while running the full set on high.
With this arrangement I don't find it necessary to include an augmented low beam auxiliary lamp but if you happen to choose such a thing my advice would be to pay close attention to beam pattern. Whatever emitter technology you choose, get one that is either reflector or projector based (as in, you can't see the emitter directly when you look at the lamp assembly) so the vast majority of light emitted is constrained to the area in front of you and not wasted on the eyes of oncoming drivers.
