I’ve started to play cs a long time ago (1.6), and I’ve been playing csgo since 2013 (I used to play more from 2014-2018 when I was in college). The game in 2013 was completely different when compared to nowadays. Map pools were different, (eg.: cobblestone/ cache instead vertigo/ancient) the maps were different (dust 2, inferno, train).
I guess that only mirage and overpass weren’t completely rebuilt. The weapons were completely different (eg.: ma1s was a monster with super fast fire rate, awp was much stronger) all guns had different sounds… so if you stop to evaluate, being a lvl10 wouldn’t matter that much, since they wouldn’t be able to apply most of their tricks. Another thing is, playing a game with 4randons and performing well with no pressure to win is completely different then playing in a squad… and usually takes a lot of time for someone to get used to play professionally and perform well… Conclusion: if the lvl 10 is super good he would be able to adapt and perform well (like pro players did migrating from 1.6 to csgo - get right, forest, fallen…) otherwise I don’t think they would be able to use their tricks since the game was completely different.