True, but when I see the word "day" I parse it to mean (assuming Earth-like astronomy) one light-dark cycle in the setting.
I get you think that, but that's not what it means (which you do agree with).
An [adventuring day] is simply the arbitrary amount of time between Long Rest recharge of class features, involving 1 or more encounters between those Recharges.
A week in town, featuring a Long rest every night (and no encounters) contains exactly
zero Adventuring days. Conversely an entire week in a hostile environment, with multiple encounters and no effective Long rests (due to the environment or time constraints) is a single Adventuring day.
Once you get that as your baseline, you can then look to modify what a [Long rest] recharge looks like to better fit your encounter pacing (number of encounters your players are expected to deal with in between long rests) to suit your narrative pacing.
If your table has 0-2 encounters most 'in game days', then you should be looking at the Gritty Realism variant - it sets overnight resting as Short Rests, and whole Weeks in town as Long rests.
Using that variant, Adventuring 'days' are likely roughly a
month of in game time each, where the PCs deal with 6-8 medium encounters (getting a Short Rest every 0-2 encounters, so 2-3 per Long rest) over the space of a few weeks, falling back to a 'safe space' to Long rest for a Week.
People that complain about the number of encounters are missing the point. Everyone has had roughly the same number of encounters at any given level, and at any given table. The question is 'when do you allow long rest recharges of class features in the middle of those encounters'.