I feel like I'm the only one that gravitates towards 8mm shank regardless of having a 1/2 motor.
Not necessarily. I really like 8mm bits, but they are not as easy to find, especially the more specialty shapes. I have to order them on-line, since no one stocks them locally....in a city of over 1 million.
I have quite a few 1/4" shank bits, because of so many trim routers. Almost all of them are really small diameter though, nothing bigger than 1/2".
For the next step up in bit sizes, I move to the OF1010, and 8mm shanks. Over the years, I have collected quite a few. It was very intentional though, because of owning the OF1010. I really like them, for a lot of jobs, where the bit is bigger than 1/4".
1/2" shank bits where my most common, until the 8mm hit that sweet spot, where a full-sized router was a bit much, but a trimmer would be overwhelmed. I used to buy almost everything in 1/2", other than the trimmer-specific bits, mostly because I could use them in the router table too.
Can you use a 1/4" diameter spiral flush trim bit in a Milwaukee 5615-20 or OF1400? Sure, but it is major over-kill. There is no point whatsoever to using a 16lb (8kg) plunge router in a situation where an 18v cordless trimmer can do the same thing.
I have found myself duplicating some of the medium sized bits with 8mm, where my original is 1/2". That way, I have a choice of router, for a particular bit size.
Take all of this with a grain of salt though, I use all of this to earn a living, in a cabinet shop. Speed/efficiency matters, where a home-shop/hobby user, probably wouldn't invest in so many duplicates. In my situation, I have at least a couple of different ways to do everything, sometimes more.