I'm responding to your popularity statement of players running characters regardless if they're good or not.

Most players do that, hence why the fusions and UI Goku have been so popular since their releases even though none of them but UI Goku are amazing.

Piccolo is ranked high on some tier lists, but Go1 puts him low.

It really depends on what their experience with those characters are. Being a top player doesn't mean you know what you're talking about all the time. A lot of Japanese players severely underrate DBZ Broly despite him being undeniably Top 3 because very few top Japanese players use him.

Beerus is low on Cloud's tier list, but Sonicfox and Go1 put him high.

Beerus is in the mid-tiers, which is where most diversity between players exists. Especially in a well-balanced game like Dragon Ball FighterZ, you're going to see some variance. That doesn't mean tier lists don't matter, you'll always see the top tiers and bottom tiers be nigh-identical, and those are the important parts.