As a diesel owner (Td6, the Lion engine which was a Ford/Pugeot joint venture and which is now offered, slightly modified, in the F150 PowerStroke), I've watched this closely for a few years.
TL;DR: YMMV
There are a couple things going on here:
1. The problem with the Ingenium isn't necessarily the Ingenium itself, it's the packaging in certain vehicles - the same engines in the Jaguar XF, F-Pace, and Discovery are having no such problems. I think the XE only has issues in heavy urban use. FIO / oil dilution occurs in most modern diesel engines because of the emissions controls that are required - specifically the DPF. I'll summarize here as such: DPFs will ALWAYS eventually "fill up" with soot. That is their job - to remove soot from the exhaust stream. There are two methods to remove the soot from the DPF, both involve heat - this is called regeneration. Passive regeneration uses high excess heat in the exhaust such as when you are driving at high load; active regeneration injects a puff of diesel fuel into the cylinder on the exhaust stroke, which then flows into the downpipe and burns (not combusts) to create the heat necessary to burn off the soot in the DPF. Ingeniums may produce more soot because they are designed run cooler to reduce NOx production, which is deemed as the more offensive pollutant and the thing that got Volkswagen in trouble. But because of diesel engine chemistry and physics, that means they make more soot. In both the US and EU, both soot and NOx are tightly regulated to the point that you can't design an engine to minimize both to meet the regulation without adding a DPF *and* SCR. That little puff of diesel in a direct-injected engine means some of the fuel (very little, really, due to how fine the vapor is in direct-injected engines) will remain in the cylinder and get scraped back into the crankcase. Packaging in the vehicle drives sizing the DPF such that regeneration has to occur more often, so more oil gets into the crankcase over time. If you only drive your diesel on short round-town trips, the DPF will fill up more quickly and more often, and since regeneration can take upwards of 20-30 minutes, the DPF may never be completely cleaned, or will require even MORE frequent active regeneration, so that even MORE fuel is post-injected and eventually winds up in the crankcase. This just highlights that diesels aren't town cars.
2. Castrol has a good name in engine oils, but the JLR spec of diesel engine oil that Castrol developed is thin for its weight and low in TBN. My Td6 takes 5W30 but it comes out of the bottle thinner than that - confirmed across multiple batches with independent testing at Blackstone Labs, so dilution negatively affects its viscosity and protection properties sooner. My local JLR service shop has just late last year begun adding an oil additive to boost viscosity and TBN. I haven't tested this batch but I'm "mid life" so will soon. JLR (and Mercedes, BMW, Porsche, Audi, VW...) will refuse any warranty claim related to engine failure or premature wear if they detect you have not used the pre-approved engine oil. VAG (VW Auto Group) was actually extremely strict with this prior to Dieselgate - they would test engine oil and then deny claims if the profile didn't match their approved brands. So far as I know, Castrol and Liqui-Moly are the only brands that carry the requisite JLR specification.
3. While there are piezoelectric systems available on the market to directly measure engine oil viscosity in the oil pan to estimate engine oil life, JLR doesn't use them (neither do the European big auto manufacturers). Instead, JLR uses software that monitors how frequently active regeneration occurs. Active regeneration is triggered by measuring the difference between the DPF inlet flow and outlet flow pressure. Once that differential reaches a limit, active regeneration occurs. The software estimates how much fuel gets into the crankcase on each regeneration cycle and then calculates when dilution will reach a pre-set maximum limit - which best I and others can tell is around 6%. HD pickups running the big Cummins and PowerStrokes can run for a long time with no issues at 10%+ FIO. My 2017 Td6 engine (again, not Ingenium) regularly over-estimates dilution and under-estimates engine oil life - sometimes telling me that the engine oil must be changed immediately when Blackstone testing indicates there is zero detectable FIO - the most I ever have had is 3.4%. However, that testing does indicate, again, that the Castrol oil, which is full synthetic, breaks down more quickly due to its thinner starting viscosity and low TBN. As a result, my 16,000 mile service interval is closer to 10,000 - but if I paid attention to the vehicle's estimation, it would be as frequent as every 3,500 miles - despite lots of long road trips and mountain driving under load. I don't know if this is happening on the Ingenium like it is on the Td6 engine, but in EU and UK markets JLR has switched to the SD6 engine which is a twin-turbo version of the single VVT in the Td6, and the problem does not occur - people are generally reaching their advertised service intervals. Perhaps they've tuned their algorithm better for that engine, or perhaps JLR tuned the Td6 algorithm to be more accurate for a "main life" engine from 30,000 to 100,000 miles when more oil dilution will occur naturally, don't know. Nothing I can download from JLR's TOPIX database reveals its logic. Bottom line for me and my Td6 engine, I change my oil on 10,000 mile intervals no matter what the car thinks it needs and I'll switch to Mobil 1 ESP when the warranty runs out - Blackstone says they are more accurate in viscosity and have higher TBN than the Castrol, but Mobil simply hasn't submitted their oils for certification to JLR's standard.
Now to the oil analyses reported on the link
@mpinco posted. Much discussion on these in other forums. Those showing "high" iron and silicon content at less than 10,000 miles are generally showing a normal wear-in profile. Those numbers generally drop off rapidly (with varying factors) after 10,000 miles. The fact that different posters are posting vastly different values for wear metals at the same point in engine life is must be approached with caution as driving style, terrain, etc are absolutely factors. For example, few seem to report whether they are towing caravans, driving in urban or very hilly environments, or how heavy their right foot is. Millers Oils is a respected UK lab so I'd put very little variation down to their process. However, the Castrol spec being thinner and lower in TBN from the start can absolutely contribute to this problem.
What can be expected in the Defender's application? None of us can know, but my guess is this. Given it's a larger vehicle with the ability to fit a larger DPF and to implement an exhaust plumbing more conducive to retaining enough passive heating to passively regenerate the DPF more often, as it is in the L462 Discovery 5, it's reasonable to expect that the Defender will not experience this issue as it will experience less frequent active regeneration.