After owning a 49 Series (I), a 68 Series II, an 87 RRC, an 88 RRC and at present an 04 DII (from new) and my wife's 08 DIII I still find it funny how I get questioned/lectured(?) on how unreliable Land Rovers are and almost always from a non-owner. AND...it's always when I am at a auto shop picking up oil for a change or at a gas station while on a 2-3 week long trip...in...said Land Rover(s).
Funny, I still don't recall anyone telling me through decades of ownership that I should buy a Land Rover for it's reliability. So...there is that.
We all know going in, no matter what series, or model, what we are in for potentially - if that makes people uneasy, which I can't blame them, then there are Jeeps, Toyotas, Mercedes, Isuzus, etc....
But...to answer the question posed by the OP:
Are older Land Rover Discoveries really that bad?
No. They are not.
But...understand what you are getting, and getting yourself into. With the internet, forums and YouTube it's nearly impossible not to know about the DII and leaky transfer cases, head gaskets...or the rust issues with Series/Defenders, etc...
Whether you are living paycheck to paycheck or on a golf course owning an older Land Rover means you have to get under it and look for leaks, pay attention to warning lights and just perform basic/routine maintenance. It's really quite simple. But for some of us, owning cars and motorcycles becomes personal and we become involved...as stated by others.
Also...not sure when owning a Land Rover became a cheap endeavor. Everyone knows going in on a Porsche, Lotus, Land Rover, etc that the parts and the labor are expensive...so not sure how some seem to forget that part of the equation.
I love my 2004 Discovery and it will be with me until I die. It's traveled with me for 20 years now and I love getting in it to go on a 2 week/2 month camping trip across North America or simply just running to get groceries. I love changing the oil in it, seeing the clear fluids in my differentials when I drain them and cursing at it trying to get new ignition coils installed. My insurance is cheap, it's been paid off for many many years and contradicting a previous post costs me nothing a month other than gas. The engine ticks a bit but when I put Rotella diesel oil back in for the summer it quiets down. I, going against everyone and everything, have never installed a 180 degree thermostat and that's living down here in south Texas, driving in Mexico and the Southwest.
So, there are things to learn and things to know and I think that's the beauty of owning an old Land Rover, or hell, any older off roader, er, sorry "overlander"
It really does become personal and I think it should be. I trust this truck when my wife is driving it to go shopping or when we are out in the middle of nowhere for days at a time with no phone reception, etc...I know I have done all I can to get it to drive and run the best that I can, and I think that's all you can do with older cars. But they take work, no bones about it.
There is quiet rewards to pulling up to a trail head and being the 20 year old truck with all the latest and greatest around you. I've got a V8 and lockers...that's all you really need.
((Although, those air vented seats and built in Apple car play are tempting!!!))
EDIT: For those considering a DII best thing I have purchased was an ultragauge and very tastefully mounted to my dash. Always know the engine temp and O2 sensors output. Food for thought...
Camping last year...somewhere in the Midwest (Missouri?):
Driving the Tail of the Dragon on my way to the North East:
Colorado/Silverton(?):