The discourse around Hall has gotten way too unwieldy here, IMO.
He's struggling badly in Buffalo and clearly the "play with Eichel for a year and pump his value" gamble isn't working, but that whole team is in shambles right now and obviously 1 goal in 19 games is a complete outlier for him.
He doesn't have great pure finishing skills - he looked like he'd be a perennial 30-40 goal guy in his first couple years in the league, but for some reason he has kind of plateaued as a 25 goal guy ever since, besides the 39 goals in his Hart Trophy season. What he can do though at a very high level is produce scoring chances by lugging the puck up ice and finding open teammates. He's struggling pretty badly right now, but I have to think based on every metric that I've looked at that this is just an awful once-in-a-career type of slump that he can bust out of, just needs a better situation to be the kind of player that he really can be. Obviously 35+ goals and 90+ points in 2017-18 was an outlier, just like his current pace of single digit goals and 50 points in 82 games is an outlier. I would say that the "real" Taylor Hall is probably somewhere in between those marks - 25ish goals and 65-75 points.
I don't know what the rental cost for him will be, but if he has a better 2nd half of the year, I think the type of production I just mentioned would be worth $6-7m x 4-5 years for a good team that has the cap space.