Question about joining a game

Can anyone let me know if it’s possible to skip the campaign by joining someone’s game during the last mission and finishing it? Will the mayhem mode open up to you after you have left that session. I’m on my fourth character and I just can’t slog through the entire campaign a 4th time just to actually play the game. Just curious if there’s a way to bypass it and yes I know I have to play far enough to unlock the weapon slots and class mods just curious if I can jump into somebody else’s game on the last mission and have it carry over to my own session, unlocking mayhem mode and tvhm without slogging through the campaign again. Thx