I hear you, but it is a mistake to underestimate the enemy. The US and its NATO allies have significant resources they can use. For example:

"NATO planes would fall down like flies."

NATO doesn't need to use aircraft. They can use cruise missiles and ballistic missiles to attack Kaliningrad, and those can be launched from many places other than easily visible NATO airfields, including from subs. The US/NATO can also focus on missiles until they destroy enough of Russia's air defense systems to start using more aircraft, and those aircraft can fly from a very wide variety of airbases and even highways. There's no just bombing "all airfields".

The US has over 3,000 ATACMS missiles. Even if Russia averages a 90% shoot-down rate that's enough to kill 300 high end Russian air defense systems, way more than necessary to wipe out Russia's one hundred or so S-400 systems even if all of them were moved into Kaliningrad.

We know the US won't use all of its ATACMS on defeating Kaliningrad's defenses, but we also know Russia won't move all of its advanced air defense systems to Kaliningrad either.

I'm just saying, Kaliningrad is in a highly vulnerable position with no easy defense solutions using conventional weapons, and the same goes for St. Pete. Conventional warfare is very resource intensive. For example, "mining ports" is much easier said than done. It would be a real mess with all sorts of incentives for one side or the other to feel they had no choice but to use tactical nukes.