I made a post earlier in the thread (with the pace this thread moves, it's surely now many, many pages ago) showing that offensively speaking, Matheson's career so far has been more productive than Petry's was when he came over from Edmonton.
When Habs traded for Petry, he was 27 years old and was playing in his 5th NHL season. Up until that trade, Petry was producing at a 0.25 PPG pace. And he only had one 25-point season up to that point. He never hit 20 points again until his second full season in Montreal in 2016-17, when he was 29 years old.
It should be noted that Petry's first full year in Montreal in 2015-16, he missed 31 games to injury and he was on a 25-point pace that season. So he would have hit 20-points sooner.
Now, Habs acquire Matheson, who is 28 years old and just completed his 6th NHL season. So far, Matheson has produced at a 0.33 PPG pace. And he's already had 3 seasons of 20+ points and had 31 pts last year.
He had 27 pts in 2017-18 & in 2018-2019. He had 20 pts in 59 GP in 2019-20 (which was a 28-point pace that year).
Petry, to his credit, was able to reach another level and became a consistent 40+ point player. We don't know if Matheson will be able to reach that level. But what we do know that so far, Matheson has been more productive than Petry was when Habs acquired him in March of 2015.
Defensively speaking, Matheson is not going to wow us. It's the area of his game he needs to improve on the most. But again, when Petry came here, he wasn't the most reliable defensively either. He didn't earn the nickname Putrid only last year.
Also, one of Petry's biggest qualities was always his mobility. Well Matheson is even more mobile than Petry ever was.
All this to say that I agree with you. There are a lot of things to like about Matheson.