When people say "#1 WR" I think most of them really mean "#1 receiving option". That can be a TE, like it was with Gronk for years. It's really about having a guy who sets the defense and makes it easier to read coverages because they can't disgusise as much when one guy is drawing so much extra attention.
Pats acquired Moss in 2007 and he was "#1 WR" level through 2009. In 2010, they had no "#1 WR" or "#1 receiving option" because Gronk was a baby, but from 2011 through 2017 he was that level of player for sure. It's not like they weren't great in 2010 still and Gronk missed time with injuries so still from 2011 through 2017 they had to deal with not having that guy and were still productive (even won a SB in 2016). 09-11 weren't McDaniels offenses anyway, so that 2010 year isn't even part of the sample size.
In 2018 he declined to the point they no longer had it and the offense really suffered that year - Brady went from MVP to game manager for most of the year. 2019 the offense struggled again, this time even worse. In 2020, the Cam Newton year, we sucked. 2021 with Mac Jones we started out ok and ending up sucking. Then McDaniels came back last year and we were very good but did fizzle out down the stretch.
Even if you look at his time in DEN, he had B-Marshall for a year as a #1 then traded him and got himself fired that 2nd year without him. And when he traded him, he did use a 1st round pick on Demaryus Thomas so it's not like he didn't place some priority on the position. He went to STL for a year in 2011, didn't have a #1 WR and his offense was LAST in scoring. When he went to Vegas, the first offseason there he made a mega-trade for Davante Adams.
For the pretty heavy majority of McDaniels time as OC here and his coaching history overall, he has had a "#1 WR". A lot of those years that guy just happened to play TE so I think that creates the ILLUSION this his offense isn't built for one. A lot of things go into it, but the years he ran this offense there were serious issues. Again, even those years with the literal GOAT in Tom Brady the offense labored through the post-Gronk prime seasons.
Having a #1 WR type player, even if it was a TE, has been something he's had for most of his history an din situations where he had personnel say it's been something he's used significant draft capital to acquire.