I see the thrust here, but it's misguided.
A default should be the baseline, never a modifier. The "oh, it's during the day, you get a bonus to sight based perception rolls" is straight out bad design.
This is objectively false.
In the first place, it's a bald assertion of principle with nothing to back it up. Sure, you can
say any given mechanic is bad design and on the basis of any principle you assert, but so what?
In the second place, it's committing a pretty fundamental error in assuming "defaults" exist when they often plainly don't.
None of bright light, dim light, and darkness are "default/baseline/"normal" degrees of lighting, from which any other kind of lighting is a deviation. They're all simply "states of lighting", any of which could happen to prevail in a given area at any given time.
None of "unencumbered/lightly encumbered/heavily encumbered" (or more fine gradations of encumbrance) are "default/baseline/normal" degrees of encumbrance, from which any other kind is a deviation from the norm. They're all simply "states of being encumbered", any of which could happen to apply to a character at any given time.
In the final place, the ultimate test of a mechanic's design quality is "is the mechanic contributing to the kind of gameplay experience that I, the designer or homebrewer, want to engender, and to what extent is it or is it not doing so?"
I'd have to say that a mechanic that makes players
actually want to care about how much their characters are carrying is a better mechanic than one that doesn't, even if the latter one happens to satisfy your (or even my!) design sensibilities. (It's pretty clear, to my mind, that you can use pound-weight encumbrance to
make players care about how much their characters are carrying, but for the vast majority of players, seemingly, it's a terrible mechanic to use if you want them to
want to care.)