fun = you don't care if you win or lose, and you don't try to play as good as you can, or you just don't care about it
If you try to win a map that's competitive play, not 'fun' play (which doesn't mean it is not enjoyable, actually it is the most enjoyable way to play, but not in public servers, or in any case not in servers with retarded beginners)
Old rating was based on frags and/or xp whoring, there was never a rating based on map winning. Nothing will change. If you want to be rated for winning a map you need to have a real team, who would like to get a bad score just because a 10 yrs old who has neither aim nor brain happens to join your team?
Maybe those 'fraggers' you hate, are actually the ones who would be able to play for obj, but they don't do it because some have played with real teams and know in comparison that playing obj in public servers is a bit stupid, while instead some beginners who think they are playing for obj wouldn't even leave their spawn alive in a real match, let alone doing something useful. So my advice is, if you want to play for fun, play for fun, nobody will stop you from doing it. They play for frags? Let them be, you can play for obj if you like. But if you want real teamplay, tactics, etc. don't play in public servers.
It would have been nice to have a custom 'tb' mod done especially for rating, and a separate ladder rating only servers with that mod, that way it would have been much easier to calculate all sorts of scores, and have players hardware ids to avoid name changing etc. But what if you give score for repairing, let's say, the truck? You will have the nub ones who repair it even if it's not necessary.