Hmm. Supposing we need a 6 hour drive at 20 kWh per hour (eschewing specific speed/distance figures), and a generous "smaller battery pack" can provide 3 hours (60 kWh). Then the generator must supply the missing 60 kWh during the 6 hour interval, i.e. a 10 kW generator.
Google says those cost from 1k to 5k USD, and they seem rather beefy.
(Just doing the math out of curiosity, otherwise agree with you.)
Not to mention, loud as all get out at that size.
It also needs a decent amount of maintenance to keep it running (or it needs to run frequently).
Personally... Ev with a swappable battery seems like a much better solution.
The only reason this even sorta makes sense right now is that we're in a really weird transition period where gas is available everywhere and it's still hard to find batteries/chargers.
This isn't a tech problem, it's an infrastructure problem. It should be treated that way.