Actually, I would say the numbers point out Nylander being a significantly better player. His play-driving ability is elite. His biggest weakness is his inability to convert on the chances he creates at a high level, but for the first time in his career, he was converting at an expected rate and it was putting him on pace for 35+ goals. This is not meant to disparage Domi, but he had his career season last year for 75 points when Nylander had the holdout/awful season. This year he had 44 points in 71 games. Domi has only cracked 60 points the one time, which Nylander did his rookie and sophomore season, and was only 1 point away from doing this year before the season was suspended.
For example, as seen here
https://hockeyviz.com/player/domixma95/MTL/1920 Domi has positive effects offensively with neutral defensive impacts, but thats actually worse both offensively and defensively than montreal without him on the ice. On the other hand, he is a good PP player. Willy was a negative on defense
https://hockeyviz.com/player/nylanwi96/TOR/1920 but only 1% worse than the team average, while he impacted offense an insane amount.
Willy's defensive zone play has always left something to be desired, but his neutral zone play, both in driving the puck up the ice, and in disrupting the opposition to take pucks away, is arguably the most elite part of his game. The fact that he led the NHL in shots from the slot this year, and tied for the lead in goals from there is just showing his dominance around the ice. Yes, he has elite linemates that Domi has never had, and domi does bring that agitator game that willy doesn't, but we know for a fact that Willy works very well in tandem with Matthews, and seems to be a great fit next to Tavares. Domi likely would too, but I'd rather keep the guy who's specialty is zone transition and slot shots despite being a playmaker, rather than get a guy who is shown in the analytics to be worse because of the agitator element.
I acknowledge what you shared with hockeyref's point shares, but the thing about point share is that it assumes equal amounts of goals and talent. Some players are better shooters, it results in your team scoring more, and some drive the net more like Willy has shown to do. Also, it shows offensive/defensive impact, but and I don't claim to know what goes into that model, but as Willy is one of the best transition players in the NHL, and the best one that the Leafs have (marner is 2nd on the team in that regard, also elite), i wouldn't get rid of that.
In the end, I understand why you want to move Willy for Domi, the agitator element is useful, and he brings an element of bite that our top six has lacked without kadri; I just wouldn't make the trade myself.