If you really wanted to use the term upgrade, you might be able to use it only for soft forks. Unless a chain is completely centralized, a hard fork is always going to cause a chain split (read that again, always). That's why we call it a hard fork.
I like that, but at the same time, how do we deal with incompatible soft forks? Like a UASF that splits from the majority hash rate chain. In a technical sense, even a MASF with extremely high threshold for activation could still eventually cause a chain split.
I believe that you could label that as a soft hard fork; I haven't seen a lot of usage of this wording, but I do recall hearing it from someone (Adam maybe).
I implicitly assume that node operators are rationally motivated to maintain consensus and upgrade the protocol. But I don't think it's my place to say what those upgrades should be or whether they're upgrades at all. That's for nodes to decide. Everything else is just talk.
They should be; but many of them are very slow.