It's really interesting question for me. Today, guys at the gym were arguing about that. Footwork, jab, control, defence... Let's not talk about achivements, because we know who wins that, but Let's talk about pure boxing skills, outboxing opponents. Who you got ?
Usyk. He's fighting people far bigger which means he has to depend completely on his skills. Bivol is on the smaller side of LHW but he's still the same stature as most LHW's and his most famous win is a against a 5'7 MW. If Bivol beats Beterbiev it might change things, but Beterbiev is still a LHW, and kind of small for he division height-wise. The reality is that Fury, AJ, even Dubious, are huge compared to Usyk and Joyce is too.
And far less skilled than boxers at LHW Which is more difficult, fighting big guys who are far less skilled, slower or similar size with good skills, faster ?
Usyk, he uses more movement, while Bivol plants himself more behind that high guard. Usyk also has better head and upper body movement. Defensively he's just more versatile than Bivol.
Usyk has superior offensive skills. Defensively is close but Usyk has faced bigger punchers P4P. Bredis and Joshua are bigger P4p punchers than the guys Bivol has beaten. So close edge to Usyk man.
Usyk for now. But if Bivol managed to beat Beterbiev, I believe the story would change. Especially if Usyk loses the rematch against Fury.
Questions like these only emphasise why there isn't only one metric of evaluating skill. Both these guys are supremely skilled but in different areas. Bivol has really sharp movement and clean crisp technique on every shot he throws, specifically the excellent spearing jab that allows him to control the exact range, pace and contours of the fight. Very solid no-nonsense defensive guard, consistent workrate and a cool head that allows him to execute his gameplans with machine-like efficiency. However, he's only had an opportunity to show those skills against men of a similar height/weight to him or against naturally smaller men like Canelo. Hard to say how well he could execute the same clinical dismantlings against men much heavier and longer than him where skills like head movement and a more full bodied style of punching are required, as well as a greater degree of strength in the clinch. I'm thinking of Gassiev to some degree here. Usyk doesn't have the clinical precision and crispness of Bivol but he's a master at fighting bigger stronger men than himself using constant in out and side to side movement, head movement, feints, angles, mental pressure and a constant and varied attacking style. He's also a master of adapting to opponents and has several times had to dig deep both into his heart reserves and into his freeform boxing brain to find solutions to problems in-ring, which is a really rare skill and where he really excels in my opinion. The only other current fighter I've seen do this to that level is Inoue, but like Bivol he's mostly doing it to men of a similar size to him. Overall I'd say it comes down to this: Bivol is more likely to put a clinic on you, totally dominate from start to finish. Usyk is going to give you chances and look ragged and vulnerable in spots. However, Usyk has proven his style works against all sizes and styles of opponent and in a variety of scenarios. Bivol, if he ever fights someone significantly bigger and stronger than him, might find himself boxed into a shell and unable to get his offence going. It remains to be seen.
Usyk. May as well just top fighting it and hop aboard. He's pretty much united every single boxing fan in proclaiming his greatness.
Bivol. We have not seen him in his top gear even against Canelo. Usyk had to dig deep in his fights to squeeze the wins.