Frankly I don't know what they were thinking with akali, since her patch before last was a buff, and she was already amazing. So they were a little slow on that.
Tryndamere doesn't get a ton of play at my level because he's pretty easy to shut down, but he's still totally viable - it's just that the type of person who picks an AD melee bruiser is not the type of person who wants to play tryndamere with the prudence with which he generally should be played, so they go with champs that require less
yomi and can do a strong gank sooner, such as nocturne.
Twisted Fate, like Teemo, is not actually supposed to win at stuff. I mean, just to take his passive as an example, it's +gold to minion farming for the whole team. That's not exactly going to help him personally do anything, since 70% of it is a buff to allies and not himself (him getting more than 30% of the team CS being an unrealistic expectation). With a power like that, he would be OP if his average stats kept up with those of his allies. That said, he's kind of a long shot if you don't know for a fact that you have some teammates with really strong farming or who will set up for your ultimate, so he doesn't see a lot of play in solo queue.
You see a pattern here? Everything has to be balanced against each other in a best-case scenario so that the top level competition doesn't disintegrate into whatever
can possibly be the most powerful given the right conditions. If certain conditions are never met a lower levels of play, then those champions never work out quite to their potential - although RIOT does their best in their champion design to mitigate these problems, and IMO they do a bang-up job.
That said, I think it's funny that even I need to point out that Tryndamere was a bad example :x but it's not because he's weak; he's just not the noct/xin type of champ that those people
want to play. People who gravitate to AD bruisers want to kill champions, period. They really don't have time for someone like Master Yi who wastes half of one skill on minion farming and another entire skill on tanking while dealing no damage whatsoever... and they also don't want a Tryndamere whose godliness is directly proportional to how much in the first 20-30 minutes you spend avoiding enemy champions and farming up minions and monsters.
