“They did exactly what we would do if we didn’t have kohanim.”
I dont know what that means. We do have kohanim. and If we didint (or if a person doenst have a bechor) then he is never mikayem the mitzvah
“The best example of them not keeping kol haTorah kulah is Yaakov Avinu marrying two sisters,”
“the best” is subjective. While it is a good question since you cant use your cop-out “They did exactly what we would do” I think the best is the Mitzvah to write a sefer Torah and a close second is Zechiras AMalek.
I suppose you can say that Yaakov wrote a sefer Torah but didnt pay attention to the words and Avrham “remembered” what the a nation that hadnt been born yet did.
But those are very far fetched. Though arguably guess these mitzvahs fall into the category of “where the ability to do the mitzvah isn’t there”
But I dont think I at any tiem disputed that
“without rejecting the gemara.”
I dont reject it either.