As a top laner myself, I can assure you that top laners are the weakest link in terms of skill, many of them are unable to perform outside of laning. That's why many top laners will resort to solo split pushing. This is not because their champion can't be used in team fights. They simply lack of skill necessary to utilize said champion.
The top lane motto is generally: I must force a stat check no matter what, if I can't kill him, I must feed him.
If you don't believe this motto, look at the Tahm Kench QQ, many champions can deal with him and kill him when played smartly. But top laners will always try to have a slapfight.
If you see a top laner in any tier, you can go ahead and assume they are at least 1-2 tiers below what the system shows.