Then you and I are talking about different things. I don't read a mathematical proof to see what formulas I can copy. I read a mathematical proof to re-use the techniques in some other domain and to understand it I have to follow along and re-create bits and pieces of the proof. Obvious mistakes like the one mentioned in the post do not hinder that process. Less obvious errors would not be caught by a linter.
As for correcting mistakes I usually go to the author's homepage to find the most up to date versions along with errata. These days most papers are put up on the arxiv anyway which is often more up to date than whatever is printed in a journal so fixes for minor errors is again a non-issue.
I'm not talking about "reading a proof to see what I can copy", it's about being able to rely on what is written there. Also, there are many papers that serve as references that I want to be able to look up quickly. Rederiving every result any time I want to use it is not the way to go.
As for correcting mistakes I usually go to the author's homepage to find the most up to date versions along with errata. These days most papers are put up on the arxiv anyway which is often more up to date than whatever is printed in a journal so fixes for minor errors is again a non-issue.