MHL can be compared to USHL, OHL, WHL right ?
If I had to make an educated guess, the MHL as a whole is probably on par with the USHL - i.e. better than Canadian Junior A, but not as good as the CHL.
The best MHL players are playing pro in the KHL and VHL, or overseas in North America. We've seen the affect of that on leagues like USHL and Jr. A where the hockey just isn't as good as it could be because the absolute best junior players are playing in better leagues.
Not unlike the KHL, there's also probably quite a bit of talent dilution and a huge disparity of overall skill-level across the MHL due to the number of teams. The MHL has 38 teams compared to the CHL's 60 teams, but potentially a fifth of the number of junior-aged players as Canada as its player-base (assuming the ratio of total registered players between the countries is the same or a similar ratio for junior-aged players). Teams affiliated with the "big" KHL clubs that have resources and money to attract the best Russian junior players could probably hold their own against an average CHL team, but not so much for the smaller and unaffiliated MHL teams.
The MHL hosted a tournament called the Junior Club World Cup throughout the '10s. It's hard to find game-by-game information, but MHL teams were the tournament winners for 7 of the 9 years the tournament ran. The OHL sent a team in 2012-13, where a fairly pedestrian Sudbury Wolves team won the tournament. MHL teams were routinely beating the USHL teams in the few years that the USHL sent a team, but only by small margins (score-wise).
In the last year of that tournament (2019-20 season), Lokomotiv Yaroslavl beat a team of AJHL all-stars in the finals. Loko Yaroslavl was the MHL champion that year and had a great team with seven players that were eventually selected in the NHL draft (e.g. Nik Kovalenko and Grigori Denisenko), but only eeked out a 3-0 win against a team of all-stars from Canada's third-best Junior A league.