The business of any particular situation being an 'automatic mayday' or whatever, in both ATC and on the flightdeck, is a result of what might be called corporate nervousness. We are moving toward an environment where everything has a procedure - if the procedure is followed then all is OK (almost irrespective of the outcome).
In the old days we trained professionals with skills to assess a situation and to make appropriate decisions - admittedly the outcome wasn't always ideal but that's life. Nowdays there is so much pressure to shorten training that we are training people what to if X or Y or Z happens rather than giving them professional skills to understand what is happening and deal with it. But at least it doesn't take so long to train them.
In years gone by I recall being faced with a beautiful summer's day, a gentle warm breeze along the runway, and the pilot of a twin-engined aircraft reporting, "just for my information really, a precautionary engine shutdown as it joined the visual circuit downwind. I put a local standby on. No drama.
A rather different situation to another that I recall on a stormy night with a wet runway and stonking crosswind and a hint in the pilot's voice that he was working hard. That one got a full emergency.
Either way I was poised to assess any further information that came to light and upgrade the category of emergency (and corresponding actions that were taken on the airfield and elsewhere) if I believed it was necessary. I always thought that was one of the things I was paid for.
Today I don't have the ability to make such choices. 50% or more power loss and I have to put on a full emergency. I guess that's progress.