I don't think there is a lot to compare the two players beyond some broad comparisons like both coming from ex-ussr system leagues that used to have some of the same issues for developing players, both players with a lot of possible development in front of them (especially tactically, as you say), or going to clubs that are struggling/began to fall apart for a time.
Mudryk's so far is a quite focused, modern cut-inside wide-attacking player in style, with some obviously excellent elite level physical attributes. The things to overcome for him to succeed at this level, besides all the usual on and off the pitch intangibles needed, seem to me to be revolving around refining (technically and especially tactically) an already quite defined style. Scouts interested in him were most likely already thinking of him in terms of a new Bale/Robben.
Golovin at cska was much more an undefined generalist prospect that looked like he could possibly develop into being a high level player in various different positional roles: centre/side midfield workhorse with good technique, maybe eventually more of a playmaking 8/10, or a dribbling/workrate focused Kovacic/Dembele type midfielder. I think the reason he drew attention from big league clubs quickly ( even before the world cup) was because of that malleability; he was doing a wide variety of technical things on a solid to very good level for his age , and he was doing it with the high workrate and willingness to press that was becoming more essential. The issues facing him moving to better leagues were different...how many of those skills would keep improving? would he end up just settling into being a jack of all trades, or an average/good but not elite player in one of those possible roles where he was showing talent? Does he have the footballing brain to bring quite a wide skillset under efficient control (especially in central areas) at a higher level and properly develop it? He was more experienced than Mudryk is right now, but still only really had the one good season behind him at the lower top ten sort of level the rpl was back then.
I'd also slightly disagree on the physical attributes side of it, he was showing great workrate and a lot of willingness to get stuck in at cska (and has kept that up at Monaco), but there were definitely questions around his ability to cope physically (especially long term) with his high tempo style if he moved to fast paced, more contact lenient England/Germany/France instead of Spain/Italy, or even just longer term in Russian league. He wasn't exactly a strong player, or a particularly fast one despite his agility and balance. Those questions have turned out to be well founded, as he quickly became injury-prone, even missing half of a season at one point. it's only in this season he's been regularly completing near 90 minutes, with Clement saying they put him on a new, specifically optimised training regime to try and get him up to a durability level able to complete consistent full games.