If implied odds were just based on stack sizes, you'd need to bet quite a bit more than 1.5x a small pot to deny them.

No, they are based on pot size and stack size, because the pot size correlates with bet sizing, which are where most implied odds come from. Sometimes, sure, you'll run up against a second best hand and take their stack. Most of the time, that's not the case and you get one or two 75-100% pot sized bets in against your opponent. Otherwise, you could call a 4x pot bet on the flop with a draw because their stack is so big comparatively that your implied odds are overwhelming.

If I have a solid hand that I will have trouble folding (like say, 2 pair, TPTK on a sorta-dry board against some idiots, etc.), I think people are getting correct odds to call a 1x pot size bet on a small-pot flop exactly because implied odds are a function of stack size and pot size, and my stack is huge compared to the pot.

I admit this thinking probably somewhat comes about from having to deal with people that will call any bet, with anything on the flop at microstakes.