This is just another case of people doing things differently and has been the case for many many years.
People have been tiling onto paint for decades, and "in my view" they have been fine for the most part.
I have been to look at quite a few bathrooms that have been tiled onto paint and the tiles have been hard to remove from the walls.
One bathroom I did an estimate on a week or so ago, had been tiled onto paint, only dot n dabbing the tiles in the corners with minute amounts of adhesive, the dried adhesive blobs were around a ten pence piece in size max, and the customer noticed some grout had fallen off from around a
tile, so as he was applying some new grout to the
tile, it fell off, bringing away 2 more with it, that's how I could see how little adhesive had been used to fix them onto a painted wall.
Now you could say, theres the proof that tiles shouldn't be fixed to paint, never mind only having maybe 3% adhesive coverage, but these tiles had been on the walls for over 25 years.
Im only saying this as some people tend to claim that if something is done a certain way, they can guarentee it will fail in a very short period of time, where it dosen't in all cases, yes it might in some, but most probably won't in most.
Now Im not saying who is right and who is wrong, and yes in a perfect world we wouldn't
tile onto paint, but in some cases it's the difference between getting a job and not getting it if a customer has had tiles on a painted wall for 20 years, then we come around and say it all has to be sanded off other wise they will fall off within the month... they just don't buy it.
The job I looked at, the customer is happy with me saying I will need a day to sand down and prime the walls, but a lot wouldn't be.
It's like using PVA as a primer.
It's probably been used millions of times, with only a few examples of the tiling failing compared to the amount that hasn't failed because of it, but it's still not best to use because it can make it fail.
So, in a nutshell, while tiling onto paint isn't ideal, the chances of it failing as quickly as some would say it will is probably very small, "in my view"