Honestly I think it's rarer to find TF and Karthus mains in bronze cause anyone good enough to play them effectively has easily "escaped" from bronze, no joke, they're just THAT good of solo carries.
As for protecting the adc, it's unnecessary in bronze usually. Just as you say bronze players can't protect an adc the same on the other side is that bronze players don't know how to properly focus targets, so if you're positioning well in bronze then you don't need your team to save you, you should be able to do that on your own if you really are better then everyone else. Just a fact.
Also 1v1ing isn't the end all be all of carries ya know. Soraka has ridiculous amounts of healing capabilities and you can single handedly win teamfights for your team if you know how to position and who exactly to heal when you have to. Obviously she can't carry as hard as say a Zed or something, but once again saying she cannot carry anything at all is just plain ignorance.
And if you still think in the "laning -> teamfighting -> seiging -> profit" mentality then sorry to say but that's probably why you're still in bronze. If you do well in lane apply pressure around the map with your lead, even if bot lane is feeding if you're a fed mid laner you should be able to sway that lane single handedly if you are good enough to truly carry and turn that lost lane into at least an even one. If you're behind and it's now what you call the "teamfighting phase" then obviously DON'T TEAMFIGHT! lol If they're stronger then you wave clear and disengage or split push while, once again, WARDING AND PINGING!
Unless you have a stupid wombo combo team comp and the enemy team is all single target and squishy or something, that's always an extremely easy way to win bronze, just everyone hit R and you win every team fight lol
For an example, say you play Nasus top, stack well and win lane because you're better then the bronzies you play with and don't deserve bronze like you claim, but EVERYONE else on your team is losing pretty hardcore, then the enemy team starts to group for teamfights. What do you do here? I imagine you usually try to help your team out and fight with them, hoping to bring your success in lane to the front and carry that fight, right? Well you'd lose that fight and everyone after that, the enemy team is stronger then you SO DON'T FIGHT THEM! Ping your team to back off while you splitpush like a monster with your Q stacks and those wards you obviously have since you don't deserve bronze. If your team is blind and they don't back off or get caught out since it's bronze the enemy team 9 times out of 10 won't push the right objectives if they push at all, so you can reply with more objectives of your own. I cannot tell you how many games last season I won as top lane Nasus by 100% splitpushing with ward coverage while my team fed and fed and fed and raged at me for not grouping. If you know what you're doing and how to play your champ you can carry almost any match... almost.
Oh yeah, and that theory of yours is wrong, bronze has always been bronze, adding more sht to a pile of sht doesn't make it any stinkier, it's still a pile of sht and smells just as bad as it always had. Also through first hand experience of working through bronze myself in season 3 then carrying 2 of my friends accounts out of it in the preseason of season 5 I can 100% guarantee it's still pretty much exactly the same thing, just on a new map.