In comparison to the 600EX-RT the 430EX II has restricted bounce capability,
True, and it's obvious that Canon intentional does this to lower models. I can't say it's affected me much, but it's also why I support having a variety of different models (if you get into flash), from the simplistic YN 460 that can't even zoom, to a 580exII that can do it all. You only need 1 flash with full rotation, anything off camera can be adjusted as needed.
just over half the range,
By my math it's 71.7%. If we're going to round so loosely I think I'd call it 75% not 50%. The 580 has 96.7% the range.
an ancient counter intuitive menu,
Mostly irrelevant if you're wireless triggers. Though I admit ignorance on the subject, I shoot mostly manual so all I do is turn the flashes up or down.
and will almost certainly never be compatible with the current RT system.
Of course not. The whole assumption is that you use some of your savings getting third party wireless triggers that don't box you into Canon's RT system.
It can't take an external battery pack, be triggered via the cheapest and most universal PC connector method,
You're right. But the 580 can. And I don't see much of a need for more than 1 (the on camera unit). If you're going to do serious studio work you need to invest in a wall unit like ABs.
it doesn't have a bounce/catchlight card.
I don't find much use in them, they're too small. If I need some bounce I'm grabbing one of the (much bigger) pieces of posterboard cutouts that I keep in my pack for this purpose. I find it to be significantly more effective, those much goofier looking as well.
It can't act as a controller for other flashes
Again, the whole point is to use third party triggers. I've tried the Canon line of sight triggering with my 580/430, and it's nice as a backup, but once you go Radio you never really go back.
and it doesn't have a plethora of custom functions and personal functions that can be useful and fun.
Like what? I feel like the majority of "strobists" that are doing creative work with their strobes are shooting manual anyway.
I'm not trying to say the 600RT is a bad flash, I'm just saying it pigeonholes you into the Canon system, where as the third party/Frankenstein approach is cheaper and leaves much more flexibility. But hey, if you have $2200 laying around for a basic four light system, have at it.