In general, 11 & 12-speed chains are not as durable for ebike applications than ebike specific chains.
Worn out chain/cassette at 600-800 miles is a bit excessive. 60 rpm cadence likely to put more stress than higher cadence.
If only tour smallest cog is wearing out prior to other cogs; longer chain may not be necessary, even with few teeth in addition to the chainring; just be mindful and avoid operating the cross chain gearings.
If preferred cadence of 60 rpm is due to physical condition, then you might be stuck with pre-mature chain wear no matter which gear you choose to use.
Lighten up the load on the drivetrain by increasing cadence may be the easiest way to reduce chain stress; even at 75 or 80 rpm.