(part 2: cuz riot has a stupid character limit)
Again, any shot caller is better than no shot caller, but those 3 lanes are your best bet at it. Top lane is usually too far removed from the rest of the team to contribute meaningful decisions, and the adc exists to do dmg, he is the secret weapon you need to aim properly, not let it aim itself.
Now, please, do not let a player's kda impact you on his ability to call shots. How many times has Link gone 0/2 or 0/4 before his team finally made a comeback? They still listen to him regardless of his kda. So why is it so important that we listen to the guy on our team that is 20/1? that just means he's been stealing all the kills, not making good calls on when to take towers and contest dragon.
Shot calling is more than merely saying, "let's team fight mid guys! I'll engage!"
No no no no no! A good shot caller would say something like this:
SC: guys, drag is up in 30
SC: nasus, you push top, we'll sweep drag tele in if the enemy engages on us.
SC: gj guys! we got drag, let's rotate bot and take a tower now!
See? it doesn't matter if the shot caller is 3/5, 1/4, 4/1 or 3/10, that was still a solid call (assuming you knew where most of the enemy was at the time)
Solo q has become hard to play not because we have become worse at the game, but because everyone is trying to carry too hard. If you want to win, you need to realize who is carrying, who is making the calls, and who is supporting. And let's face it, you can't always carry. And the guy that is carrying isn't always great at making calls. We need to learn to be more cooperative and less. "the only way I'll win is if I carry myself" and more "okay, I'm not doin so hot, but this guy is doin great, lets rally around him and try to take objectives. I'll do my best to keep him alive in fights"