I think you're right, it's what we were used to as first level characters. Although, geeky as I am, I always created crap in my head about all my first level characters and was sad when they died.
I would usually have an idea for what I wanted for the classes I liked, and just keep playing that until one of the characters survived the first few levels. As I recall, Pharesm, my 0E illusionist of ungodly power -- he was something like 12th level when retired -- was actually the 8th or 9th "Pharesm mold" character. The others never made it past first r second level. Even with the mold, most of (the surviving) Pharesm's personality came from things that during his early adventures, not from any pre-planning on my part.
Side note: I still can't believe I got an 0E illusionist to name level.
I think that because I use Vancian Magic as opposed to HP/Magic, it would be OK.
If you use Vancian magic, I don't see any reason why your hit point revision shouldn't work well for all M74 classes.
Thanks for the comments - I'll give it a try and see how it works.
That's always the best way to handle major rules fiddling: try it and see it works as expected.