[imgr8ness]

Roughly the same as security through obscurity, which doesn't work. Not to say custom ROMs don't have benefits, but I'd never choose a solution based solely on whether it's "mainstream". Longstanding support and support for Google services are why many will stick with a stock ROM. GrapheneOS is specific to Pixel devices and it's a small team, so there's no guarantee you'll receive support in 5 years.

"...why many will stick with a stock ROM."

I assume my audience here are not people which would be regarded as part of the 'many' when it comes to technical discussions, therefore what the 'many' would do is of no interest to me.

"GrapheneOS is specific to Pixel devices and it's a small team, so there's no guarantee you'll receive support in 5 years."

Of course, but this is based on the assumption that someone using GraphenOS or any other alternative would never consider another option and therefore be at a disadvantage when that choice falls behind in updates. However, any person who is involved deeply in field of computing will know that you never stay put, technology is always changing and a good technologist will always be looking to expand their knowledge and grow.
Computing is not a stagnant field, if you do not keep up with the many changes then your knowledge quickly becomes outdated.
Which brings me to my point, whether a particular OS loses support in 5 years time is completely irrelevant, as any real techie would of probably tried 5 different types of alternatives by that point.

My original point was that Android was a more viable solution for privacy/security than iOS. GrapheneOS exists because of Android being open source, and therefore modifiable. In 2022, being able to flash a custom ROM doesn't necessarily make you a technical user.

Consistency being an important factor in anyone's decisions, there can be value in the ability to deploy and rely on a single ROM long term. Perhaps you enjoy changing ROMs every year, but every use case is different. CyanogenMod lasted for many years, so it's possible for Custom ROMs to thrive.

I agree with what you're saying. For me at least, I can't see the what the overarching point is that you're trying to make.

Referring to my original statement about using a custom ROM, and to expand upon that, if you value privacy AND security then I suggest a custom ROM if you are technically minded and have the will.

You've mentioned that '...security through obscurity doesn't work...', and on that point I have to disagree.

The alternative being, in principle, to mask yourself by 'hiding' amongst a group. This has its uses and for most people is probably the most practical. However it is to say that you are essentially playing the odds.

I prefer to rely on myself as much as possible, certainly not place my security and wellbeing solely in the hands of a multinational corporation. If that is in fact what you're suggesting.