I have a lawnmower, a very large outboard motor, and a generator that all prove your point about ethanol being bad for engines it is not made for. I’ve had to have all of the unplugged and reworked.
However, and I’ve been told by those mechanics that ethanol reacts with the plastics/rubbers in those engines, but that different categories of plastics are just fine.
I have yet to buy one of those newer ethanol accepting engines, so I’m just going on hearsay from mechanics and from my reading.
Yes, the effects vary. On 2 cycles the very thin plastic gaskets, flapper valves and rubber hoses and gaskets tend to degrade. I have extensively researched, replaced and now have rebuild kits for all of them.
I ended up buying a sensor reset tool to stop the O2 engine sensor “warning” lights. Cheaper than replacing one for $100 every six months.