I'm a big fan of Kofman and Lee, but I take their estimates and impressions with a grain of salt.
I think that they are by far the most reasonable and accurate analysts from the West when it comes to this war, but they are still from the West (as am I, just to make it clear, I live in America). They still don't veer into wrong-think, and present a picture of Ukrainian superiority.
I think it is possible that Ukraine has favorable attrition (particularly in Bakhmut) but I don't think it's very likely.
Some other comments, like the supposed superiority of Ukrainian infantry over Russian infantry. I find that questionable. Sure, some Russian conscripts have almost no training. However, the quality of this force varies. The most funded and elite volunteer/conscript units are clearly put through lengthy training before deployment. The level of troop quality clearly varies depending on where the units come from.
By contrast, as Kofman and Lee describes, Ukrainian conscripts are taken off the streets or they volunteer. The most elite units get their pick of conscripts. The level of training is not well-described. Therefore, I am inclined to believe that there is almost no training given to conscripts. Aside from that, some 18,000 troops were given NATO training for several weeks, though there are obviously problems with that training as well.
On the balance, I am very dis-inclined to believe that Ukrainians are inherently better at infantry action or that their attrition ratio is enviable. Again, it is certainly possible, but I find it highly unlikely.
What is most likely happening, is that Kofman and Lee are being fed information by Ukrainians, that Ukrainians want them to know. This'll be a combination of anecdotes and beliefs that's a mixture of accurate/fictional. It'll also probably come from many junior officers who are unlikely to see the bigger picture (doubt that Syrski personally met with Kofman to discuss the situation). I'm sure that Junior officer from an airborne brigade thinks Russians are shit at infantry actions.
Well yeah, if his elite unit, full of the best conscripts with the best physical condition and the best training, regularly destroys the most expendable Russian units in trenches, I'm sure that's the impression he has from the whole war. I'm sure he thinks that his supporting artillery company is the best in the army, but have they ever gone head to head against Kaskad, who have routinely bested Ukrainian crews?