[oil pan 4]

Actually NEC allows you to run 15 amp receptacles on a 20amp circuit so long as you use 12ga wire.
That's about the only time you will see a smaller receptacle on a bigger wire and bigger breaker for every day normal use.
The 5-15 and 5-20 receptacles aren't really the problem they can handle a lot of power, I have a dedicated welding outlet, which is a 5-20 outlet on 10ga wire and a 30 amp breaker, its even labeled "welder only" because that's all I had room for. Its one breaker, one receptacle on about 9 inches of 10ga wire. I can do this with a welder because the most it will ever run is a 50% duty cycle.
Most welding machines call for a 60amp or way smaller breaker. No need for separate connection for most machines.
EVs, block heaters, deicing heaters are all 100% duty cycle.
If you have to put in separate service for an electric vehicle that's an extra service charge per month you will be paying for.

To hook up grid tie to your house put a sub panel out side for it or run it back to the main and put it on its own breaker.