I already answered. For $4 million his performance and pace this year are outstanding. As I asked before, what are you expecting from him at $10.5 million in a few years? Just so we can be clear about how to assess his performance using your methodology of cap hit vs. actual salary.
I am not sure if I can provide an answer that you would deem satisfactory. I agree with cap hit as being the appropriate measure generally speaking but I do think there are specific contexts when it may not be the best metric. I think when a team is closer to the cap ceiling then evaluating player performance based on cap hit is most appropriate. This is because cap hit is a real constraint in that situation; there is a finite amount of cap space and therefore each player's performance is measured relative to how well that cap space is utilized and could be utilized.
Alternatively in situations where a team is near the cap floor each player's cap hit is fairly inconsequential in that given season as there isn't really a cap constraint to contend with. If those cap floor teams have an internal budget then actual salary could be scrutinized as it represents an actual constraint; each dollar spent creates an opportunity cost of how that same capital could have been spent differently.
I also think a player's age is important when evaluating a contract. In a max length, or near max length contract a young player should show progression. In such a circumstance a team pays for some projected potential with hopes that it is attained. The organization may also be comfortable with some variance in performance as they may feel they underpay the player in some seasons and overpay them in others but that the compensation balances itself out.
I also don't think it makes sense to evaluate a contract in isolation. The quality of the contract is not just determined by player performance relative to cap hit or salary, it is also measured relative to what the market determines is an appropriate cap hit and salary for players of a similar performance and having similar attributes.
But to your exact point Tkachuk makes $10.5m in 2023-24, 2024-25 and 2025-26. He will turn 24 at the start of that compensation. What I am expecting during that time frame is something similar to Jamie Benn and Mark Stone in terms of performance. What that means is close to a point per game or slightly over it while also providing non point related contributions (defensive play, physicality, etc) at a very high level. During that same age range Benn put up (2013-14: 81 GP 34 G 45 A 79 PTS, 2014-15: 82 GP 35 G 52 A 87 PTS, 2015-16: 82 GP 41 G 48 A 49 PTS) and Stone put up (2016-17: 71 GP 21 G 32 A 54 PTS, 2017-18: 58 GP 20 G 42 A 62 PTS, 2018-19: 77 GP 33 G 40 A 73 PTS).
Both Benn and Stone's contracts after those performances had a higher cap hit and higher peak salary than Tkachuk's. Benn received a $9.5M cap hit with $13M in salary for the first three seasons of his contract. Stone also has a $9.5M cap hit with two seasons of his current contract reaching $12M in actual salary and another two reaching $11M. Both have also received massive signing bonuses as part of their contracts with Tkachuk's contract doesn't have.
Those two may have had to prove more offensively before receiving big paydays but I think they are decent comparable for Tkachuk. If Tkachuk puts up similar numbers to Benn during the same age range while also bringing peak physicality, improved defensive play and outstanding leadership, I would be ecstatic.