The hydrocarbons are going to get burned one way or another, you can just trade one type for another types.
You cannot replace most oil-based fuel with incinerators. So I'll disagree there.
The utility of oil-based fuels is the energy density in combustion. Burning plastic doesn't come close to the same exchange.
The energy density of plastic (by weight, not volume) is virtually identical to that of oil.
Yes, the machine used to burn oil vs plastic looks different, but coal plants can burn plastic without much modification - and they would be much much cleaner than coal when they do so.
Oil-based unleaded fuel is not oil. You probably could run trains on plastic. That's if you didn't mind hot plastic raining down around the tracks as the coal dust and soot did when we used it for trains.
They burn MUCH MUCH cleaner that coal for example.
> The energy captured from the burn is obviously not the same
There is nothing obvious about it. I don't understand what you mean? Plastics have around the same energy density as oil.
And even in the lofty goal end state of zero fossils, if it's not a complete collapse back to medieval tech (and population numbers), we would likely end up with biomass based plastics serving as packaging and the like at the upper end of that carbon's energy slope, before utilizing the remaining bound energy in an incinerator.
Biodegradable properties of grown plastics are only a last line of defense against pollution when collection has failed.