There really is an order of magnitude difference in the complexity.
The typical ICE already has electric batteries and motors. But the EV does not have the ICE parts. No dealing with oils either.
And the fact that non-yokels also build cars, does not diminish the point.
Building an ice vs electric vehicle in the discussion context means design plus build, not a kit or retrofit. It's a bit different.
Note that in 1900 the electric car was also seen as viable and people were building it. For "reasons" the ICE took off, while the electric car remained as mostly a thing people did in their garage.
(Most diaries and reports at the time seemed to imply that the DIY car people of the early 1900s much preferred the simplicity of the electric car and had some miracle happened at the time in battery chemistry the world would have shifted a much different direction.)
- The oil lubrication system, starter/alternator, various belts, and gearbox (if front wheel drive) are typically part of the engine package so don't really impact complexity.
- Liquid cooling is required for EVs if they're going to perform equivalently to a modern ICE car.
- EVs contain high voltage / high current wiring that needs to be considered carefully in terms of crash safety.
I'm not against EVs here, I think they're great. But if you want more than the old "drop a forklift motor and some batteries into a donor car" DIY build, an EV isn't actually that much simpler to assemble.