Checked in for our first Easyjet flight since 2019 and our own experience supports the OP’s hypothesis.

Myself and the 12 year old were given 9A & 9B for a flight just under 3 weeks from the check in date. This flight is completely sold out. I booked myself a bigger cabin bag along with the tickets in Feb.

MrLapLap, travelling alone with small bag only, checked in closer to a month before the flight date and was given an aisle seat in the mid twenties. That flight still has £150 tickets available.