I wasn't terribly upset when the Leafs elected not to re-sign Gardiner because I expected his cap hit would be too high to fit (we still had Zaitsev on the books at the time) and because I didn't have as high an opinion of him as some here do.
Most of the time he's a very decent defenceman with excellent analytics (as well as "old style" stats) but from time to time he'd make those nasty misjakes, and their likelihood of happening seemed to be directly proportional to the pressure of the situation. I've talked about this a couple of times, recently, where playing in high-pressure situations can mess with your head, and Jake always struck me as someone who didn't handle it very well. His most egregious moments seemed to happen at the most inopportune times. He would also do jaw-droppingly amazing things at times, so I always thought of him as a "pick your poison" player and completely understood why others liked him more than I do/did.
By any objective measure he's far from being a bad defenceman and I'd happily take him at his current $2ishM cap hit over Zaitsev at $4.5 or Ceci at $4.5. I'd take him every day of the week over dozens if not hundreds of other NHL blueline regulars. There are also dozens I'd happily take ahead of him, but most (none) aren't available and most are significantly more expensive.