The screen area is slightly smaller but the device itself is much smaller, which is a good trade-off. The processor may be "mid range", but I'll take a 2020 mid-range SoC over a 2017 flagship one any time (the 700 series have always been a good balance of computing power and energy efficiency). And yeah, forget the excuses that various manufacturers have made, removing the 3.5mm jack was always about increasing their margins and of no benefit to the user (I always think it telling that Apple started it just a few months after they bought a popular headphone manufacturer - I'm sure they hoped to benefit from driving people to bluetooth headphones).
My Pixel 2 is still working fine apart from the battery life not being what it was, so on environmental grounds I'm so far resisting upgrading to the 4a. But if anything happens to it (or the battery lets me down in a bad way) then it's a no-brainer indeed.