I think RTW did do characters better, ironically enough, or at least make you care about them more. I also liked the way they split Rome into sub-factions but that was one of the most hated features of the game so...
I think there's too many characters popping up that you don't care about in both Paradox games, and in any future game in this series, I'd like to have the ability to sort characters, demote and promote them between these groups.
One group are my active characters (limited to a max size based on your empire size, like in TW) who work like characters normally do, sort of like the main cast of a film.
Then I'd like a box where my 'supporting actors' go, these are the guys I care about but not that much. They still age and maybe minor things happen to them, but I definitely don't interact with them as much, and they generally stay in the same circumstances as I left them, ready to move up if something happens to one of the main cast.
The third category is the characters I'm done with. I don't expect to see them ever again, but once in a while the game wants to pull a surprising plot twist and reintroduce them much later on with an interesting story of what happened, I'd consider taking them back into the cast.
The fourth category is my prospects. These are where the game presents new characters (of whatever age and situation) that I might be interested in. Sort of like my actors guild that I can pick my cast from. A permanent 'man of the hour' pool from RTW, again limited by some game variable.
As an aside, I find it really amusing the way people use the term grand strategy/grand strategy game. If you ask on Taleworlds, Mount & Blade is a GSG. Total War forums...yep, GSG. The Steam user defined tags are even better.
City Bus Manager - GSG
Conqueror's Blade Colosseum (a Roman ninja slasher game) - GSG
Beaver Clicker (a clicking game to collect logs....) - GSG
It's just a silly category. It's basically every game that has strategy and isn't Starcraft or a game like that, but I'm sure you'll find someone who says Starcraft is a GSG too.