Entry level M1s really should start at 16GB and could end there. Hard to imagine that anyone would ever need more beyond it’s expected life cycle and easy to conjure reasons 8GB will eventually be inadequate. The biggest problem with the current design is it’s single monitor limit notwithstanding some of the, at best, awkward work-arounds that people have been promotingMaybe.
There's lower latency, higher bandwidth, much faster single-threading, etc. You're comparing a 2012 machine with a 2020 machine, so there are a ton of factors that are different beyond the RAM being unified.
There will absolutely be tasks where an 8 GiB machine is forced to swap where a 32 GiB one isn't, for very obvious reasons.