You raise some good points. I find that it's hard to find information on the topic as a whole because a lot of sources have fairly big biases - either pro or anti EVs - which often times aren't very transparent. And also because you usually have to dig deep to find an example that fits your situation. For example, on the topic of your last paragraph, when comparing cars to motorcycles, what's a "car"? Are we talking about a two seat Clio or a four seat family wagon? It gets even worse with motorcycles given the big variety of engine configurations.

Some years ago I read something similar to your last point - that in general, motorcycles produce a fair amount more greenhouse gases than an average car. More recently I've come upon an article that tested different motorcycles with different CCs and engine configurations and the results were a lot more nuanced. They mentioned that 2 stroke motorcycles were basically awful in terms of how much greenhouse gases they released. 4 stroke motorcycles, on the other hand, were comparable to a small car. Small and medium CC 4 stroke motorcycles would win out against the average car in terms of emissions, whereas bigger CC 4 stroke motorcycles would emit slightly more greenhouse gases than the average car.