This is hard to predict, realistically he can beat all of the above, but I think that Povetkin and Kabayel would be his toughest opponents...
Think Parker would lose to Haye, Povetkin, Kabayel. I think Parker would struggle style-wise with Ortiz but would be a close fight. Parker beats Hrgovic for me.
He beats Ortiz while it would be tricky because of styles, Ortiz would fade late like he always does and Parker takes over in the 2nd half and stops him. Kayabel is a hard one to predict. Kabayel looks more versatile of the two right now, but he hasn't faced anyone as good as Parker or with Parker's speed, so I wouldn't right Parker off. I'm leaning towards Kabayel. Povetkin on gear beats him, Povetkin off the gear probably still beats him but makes it close. Haye I think gets a little underrated because his resume is so thin. But I think Haye did his best when opponent came to him and Parker now is more a cagey fighter who picks his spots. So I think Parker beats him because of styles. Parker beats Hrgovic. Hrgovic is too predictable but he'd give Parker a good fight.
Prime for prime I've got Parker against all of them except Povetkin. Parker just has more varied and deeper experience and a versatile style paired with a solid chin and gas tank and power when he wants to. Kabayel could beat him, but I haven't seen enough from him to say that, he hasn't fought someone with decent movement yet (crippled Sanchez doesn't count), and his defense is lacking in that he takes too many punches to unload his offense. Ortiz and Haye would probably be relatively boring fights as Parker does enough to stay in the fight and slowly take over later on. Hrgovic is too straightforward for Parker and I think he will have the strategy and tactics to to dismantle him. Povetkin is tricky and tough as nails with power as well, and I think he could surprise and shock Parker a bit. I could see Parker giving away too many rounds while he rallies that he loses a decision.
Might have a good showing in one or two of the fights but I expect him to go winless. Doesn't mean he would but I expect him to.
I think he beat hrgovic. The rest in their prime i think he loses but only just. To be fair they are all really good close fights which I think shows parker is a similar level. Haye at cruiser was a different animal by the time he moved to heavy his body was done. Prime cruiserweight Haye splatters him.
A lot of close fights, but can only really see prime Povetkin beating him tbh. Maybe Kabayel but it would be razor close.
Luis Ortiz- Wins UD Agit Kabayel- Loses UD Alexander Povektin- Loses UD David Haye- Loses UD Filip Hrgovic- Wins UD Hardest one to call is the Kabayel fight, because he is only half way through his career and we do not really know how good he is.