While my top 5 not including shaco because i dont know how it affected the patch is Yorick, Poppy, Ryze, Warwick, Vayne.
He is hands down the best caster, with low cooldowns full power, can 1 on 1 no problem, scales well during the whole game, push well, he is good against assasins and bruisers , or at least better than most casters.
Basically he is the best Ap nuker in dominion since he can fight non stop and deal with most champs, he is one of the champs in dominion that isnt scared of anyone. That puts ryze that high.
The argument that they are waiting for it to be balanced its not truth, at least not as worded "as well as they can" every game can always be improved on balance. If game developers would wait for that moment, games would NEVER EVER be released.
So thats not the reason, im not sure whats the reason but thats not it.
You are right about the ranked stuff too, I honestly don't know when it is coming, I'm just making an educated guess; Dominion is young, give it a chance. A more accurate reason would be that they are waiting for season 2.