Povetkin is a mandatory there is no reason for him to risk another hard fight until he gets his AJ payout. Of the guys you listed I still favor Povetkin over all of them but time not on his side
Parker proved he is better than most expected. Parker matches up well with both Ortiz and Povetkin and has a good chance if winning both, especially Povetkin.
Parker can use angles and does possess a good amount of power. Sasha' offense can get nullified if you keep him at range with a good jab and a good 1-2 combination. Povetkin would have to take some risks to get it on Parker, if not he will get outboxed or even stopped later on.
Povetkin is better today than he was at 32, when he fought Klitschko. Now he has head movement, lateral movement, his ring IQ much better, and he hasn't lost any power. Not sure if he beats Joshua, but he does a much better job of cutting the distance between him and his opponent and getting on the inside than Parker... Parker had no plan, he just ran in there and started throwing haymakers, hoping something would land. Povetkin would be more calculated.
I would take Sasha in Russia to win but not the UK. Joshua would be pretty confident of another decision. You saw those opening and mid rounds tonight, nothing in them at all but virtually all scored for Joshua. Sasha is still better than Parker for me but it's a big ask.
Then you realize Povetkin isn't better. He is just on more steroid now. Alexander was almosnt knocked out by David Price. If Price was in shape he would of probably beat Povetkin. There was never anything special about Povetkin. Just another European hype job who spent the vast majority of his career fighter other European bum fighters. Wlad is a good puncher but was so timid once he got knocked out a few times. If Wlad was more aggressive he would of stopped Povetkin easily. Guys like Deontay Wilder or AJ would stopped them if they jumped on him as well.