do tiers matter?

Brotherhood is way more important than tiers. If you like the guys, join.

It really depends on what you are looking for from Greek life. If you want to party with the coolest people/girls in school then joining a bottom tier may affect. But if you just want some good friendship/brotherhood then just join whatever you feel great about

Most fraternities mix with some sororities. There are ~200 girls in a sorority. Let’s say the frat mixes with 2-3 sororities, that’s 400-600 girls, though obviously not all of them will go out/be your year/etc. Point being, if you wanna party with girls, most fraternities will have quite a few girls with some you don’t like and some you love and everything in between. If you really like the guys, go for wherever you’re happy.
The tier system really DOES NOT matter if you like where you’re at; it’s just people who wanna feel better than others based on stereotypes. There are gorgeous/cool/fun people in “bottom” frats/sororitys and less conventionally attractive/weird/boring people in “upper” frats/sororitys.