I saw another study that had the USHL much higher, which I believe, given the number of draft picks (and NHL players coming out of the USHL, and especially the USNTDP.
I'd think the USHL is at least equivalent to, if not better than the CHL, these days, a bit younger on average, but with the flood of American talent, the talent pool is probably less diluted.
Their top guys are really good. And the league *was* lower scoring for a long time until the last couple of years, which meant some good players were under-drafted.
But the bottom proportion of the league drags it down... partially due to the lack of decent players aged 19-20 in general meaning they have guys in the bottom six and bottom pairing that would not make many CHL teams and instead would be BCHL/AJHL etc. Almost all the top guys go to the NCAA or are pro's quickly and dont hang about a year or two like in the CHL.
If you are doing an NHLe based on the guys who actually make the NHL, then the USHL is really solid. But when you look at the league as a whole and where the players actually end up, and how they do there, the quality is less if that makes sense.
That is because while the USNTDP is great, and will have ~10 or so future NHLers on each year, a lot high end, even the "premier" USHL teams outside of them might have ~2-3 future NHLers on their roster in a very good year.
Put it this way.
If a non-USNTDP guy is scoring P/GP in their draft year they are likely as good/better than a CHL guy with similar. But the overall quality of the league is worse still.