Until that Upamecano gaffe that caused the second goal I thought both teams were fairly evenly matched. Both teams created chances and could have scored, wouldn't count the Gundogan chance as one as it would have most likely been ruled out for a blatant foul on Sommer. Sane missed some really good opportunities to score or play his teammate in, ofcourse. Feels ridiculous to say but Choupo Moting is arguably one of their most important players now, Bayern completely lacked any focal point in attack without a striker (Mane has just not worked as one this season).
After that second goal Bayern just shut down mentally and got away with just conceding 3 goals. As I said, they're always due a defensive implosion. Upamecano is a the French Lucio, talented but utterly brainless at times and needs a manager to discipline him.
No chance Bayern get anything from a second leg other than a bit of respectability.