How does that change the fact that DeAngelo has exactly one season of putting up more than 30 points at 24 years old, while Ristolainen has 4 confirmed seasons of 40 points at 25 years old?'
I don't get why this is so hard for Rangers fans to grasp:
Tony DeAngelo is a one-dimensional offensive defenseman who can't play defense, the Sabres already have that.
Tony DeAngelo has a confirmed history of toxic behavior, and a young team like the Sabres who's GM has openly said they were looking for "character guys" to surround the young talent with aren't going to want someone like Tony "Will run through a wall for a teammate, while screaming racist/homophobic slurs at teammates and officials" DeAngelo
He's had exactly one good season in his career.
The Sabres have too many RD and Tony DeAngelo is not worth trading our best prospect for. He's not worth trading for on the Sabres at all. It's as poor a fit as you can get.
You can't beat the context drum and ignore the context you don't like. Yes, Risto got 40+ points 4 times. All four times, he played a largely complete season (82, 79, 78, and 73 games respectively). DeAngelo "only" put up 30 points two years ago--but he did it in 61 games. Last year, DeAngelo scored 53 points (8 points better than Risto's best season) in 68 games.
More context--goals tend to be valued more than assists. DeAngelo scored 15 goals last year--almost double Risto's career high.
More context-- All four times Risto put up 40+, he played WAY more minutes than he should have (25+ minutes per game in three of those seasons, 24:38 in another). DeAngelo? He played just over 19 minutes per game the last two years. So Risto put up 40 playing nearly 7 minutes more per game, and (as mentioned earlier) playing ~20 more games than DeAngelo's 30 point season two years ago. Color me impressed.
More context-- All four times Risto scored 40+, he seemingly didn't even TRY to play defense (-96 collectively over those four seasons. His best season before this year's -2, he was a -9. Those are his only two seasons that he was under double digits on +/-). I tend to think +/- only reveals anything in the context of how other players on the same team performed. Aside from his -9 outlier season, his other 40+ point seasons saw Risto with a team worst +/- twice, including a -21 (nobody else within 5) and a -41 (the next worse player "only" had a -22). His other 40+point season he was -25 with only two players worse. DeAngelo? He was a +12, while being stuck with Marc Staal all season. He was a +6 in his 30 point season. He used to be a miserable defensive player on the scale of Risto, but--and this is a key difference here--the Rangers' coach sent him down to the AHL and wouldn't trust him as a regular until he addressed that issue and at least tried to play passable defense. Risto never addressed his defensive issues. DeAngelo has.
Regarding your other "points"--I don't know how many years are considered "long enough" so that you aren't judged by what you did as a teenager, but mid-20s seems like more than enough time. He's been a model citizen on this team for several years now.
And as has been mentioned before by others, he was traded by Arizona because the Rangers targeted him and offered their mid-20s 1B center and a top young goalie to get him (and a 1st). The reason people are looking to trade him now is that Rangers fans don't want to be in a Tampa Bay situation. The Rangers are committed to Trouba, they have Fox in the fold already, and both Nils Lundkvist and Schneider near the top of our prospect pool for RD. Better to move a "final RFA contract" player at a position of absurd depth for a player on an ELC. Otherwise we'll be setting ourselves up for an offer sheet on Laf when he comes up for a second contract. If the salary cap weren't a thing, you wouldn't see a single Rangers fan trying to move DeAngelo.
That doesn't mean Buffalo fans need to want to trade for him, but you should at least refrain from this "ONLY 30 POINTS ONCE HUR DUR" nonsense. DeAngelo is at least a full tier better than Risto as a player. Putting up 40 points a few times because your team is incompetent and plays you 25+ minutes a game isn't exactly a point of pride.