Can I just add here that even if Einstein were a plagiarist or not, does it make any difference? Suggesting Einstein may have plagiarized someone else's thinking is a subtle way of giving credibility to the idea that was plagiarized. Why bother plagiarizing someone if the idea was pure nonsense anyway?
You're right. It's sort of beside the point. We all went to school and plagiarized subjects, didn't we? We did that in order to learn and understand the subject, really in order to discover the ability to think within and practise the relevant discipline.
In the case of physics and engineering this DOES involve considerable work and a certain fluency with mathematics. Einstein may have had a tendency to avoid work, and maybe was no mathematical genius, but he networked constantly with the top physicists and mathematicians of his day until he had produced something which NOBODY had been capable of, something which even now remains the bedrock of physics and cosmology.
It's not the person. It's his ideas. And they are hardly wrong at all. Except that they aren't a Grand Unified Theory.
How wrong is Science? This vid makes important distinctions with respect to "wrongness".
Of course you have a right to be wrong. You may play the following in YT - embedding has been disabled.