One reframe that helped me: the shoes are not competing with your other clothes, they are competing with the trip you are actually having.
You said a couple of days of trails inside two weeks of cities. Two days out of fourteen is not a trail trip with city stops, it is a city trip with two exceptions - and paying a third of your bag for two days is a bad rate unless those two days genuinely need a different shoe.
Worth asking honestly whether they do. A decent trail shoe is fine in a city and looks unremarkable almost everywhere now. The reverse is much less true, which is why "wear the bulkiest pair" is the standard advice - one shoe that covers both ends is the version of this that costs zero.
If the two trail days involve something a trail shoe is genuinely required for, that is a real constraint and you carry the second pair without guilt. But that is a small number of trips, and most people packing a spare are hedging against a version of the trip they are not going to have.