I actually was not familiar with the sources you quoted, but there isn’t a contradiction to the rambam and there’s no second-coming-after death or partial accomplishment either. Rashi compares it to Moshe rabbeinu, who was known to the yidden, but had not done any redemptive acts. He then was hidden and returned, so these opinions in chazal(which are not standard in achronim who talk about bias hamoshiach) are saying that moshiach will be known, and then disappear, and then return to redeem us.
But no one said a word about dying. Because that would be disqualifying, as was the case with bar kochva. As soon as he died, everyone agreed he was not moshiach. They didn’t say that he would return.
And the rambam is clearly talking about retaking eretz yisroel, as he says all of the enemies “misaviv,” surrounding us, paired with “gathering all of the exiles”…bar kochva was most certainly fighting to retake eretz yisroel and restore Jewish sovereignty, as will be the case when the real geulah happens.