Ullmark was 2.5 years younger than Campbell will be when he signs his next UFA deal.
5.25 mill is 6.36% of the 82.5 mill cap. That would be breaking the market for a goalie like him, which caps out at 6.1% for Ullmark, Varlamov, and Lehner for guys who signed in that general age range (Campbell would be 6 months younger than Varlamov, but 1.5 years older than Lehner and 2.5 years older than Ullmark when they signed). Ullmark was a clear overpay too, because Boston was desperate when Rask semi-retired and it was between him and paying a 1st for Kuemper.
Lehner and Varlamov, meanwhile, both had multiple years of starting experience with high end results. Lehner was even coming off of a season where he took his team to the Conference Finals with a .918, and had a .930 season the year before that.
Campbell would have had 1 year + 1 Covid year of (great) starting experience, and so far, has only choked away a playoff series. Short of Campbell winning a Vezina or Conn Smythe, he is getting a lower percentage.
I anticipate he gets 4.75 mill on a 4 year deal right now (at best). He needs to maintain his current play and have a stellar playoffs to get more than that. 500k is not much, but that is 1/3 of your overage. The other 2/3's comes from picking between Ritchie, Kerfoot, and Kase (who may ask for more than 2 mill anyways) and giving Sandin his QO for one year rather than paying him more for 2 years. That should also give us enough money to get a cheap-ish #7.