MOT_THST_HOVER has much less impact than you probably realize. It’s used to set the thrust “center” point in manual modes (stabilize/acro) to ease the transition from assisted modes (alt hold, loiter, auto, etc) and give the user a consistent “feel” between different vehicles, with a consistent hover throttle at the RC stick mid-point.
Enabling the hover learn parameter as directed during the first alt hold flight should correct it, at which point you can look at the result in either a log or the newly saved parameter.
The real implication of a higher value – higher than most copters will require, is that a switch from an assisted mode back to stabilize (with the throttle stick centered) will more often than not result in a climb rather than a descent until such time as MOT_THST_HOVER is learned or set more precisely - likely a bit of insurance on first flights to keep vehicles with low thrust to weight ratios from plummeting downward if hover throttle is not learned, and the user switches out of alt hold.
It seems that you are implying that the default is to be somehow interpreted as a desired value. That’s almost certainly not the case. My understanding is that it is set to 0.35 for the reasons above.
EDIT:
However, the last change to the default that I see in the source code dates back to 2017, where the default was REDUCED from 0.5 to 0.35. I do not see any changes from 0.25 to 0.35, but perhaps I’m missing something.
The reduction was to keep vehicles with high thrust to weight ratios from having too “twitchy” a throttle until the parameter is appropriately reduced, thus reducing the perceived “fly away” effect that can happen with a high MOT_THST_HOVER when switching out of an assisted mode.