the game came out like 2 months ago and we're already making tier lists srsly
also tier lists don't dictate whether a character is good or not, it's the player
i agree tier lists aren't the be all end all in most scenarios, esp when you're playing semi casually
but if a character is at the bottom 3 of the tier list (which I've seen Mii Gunner at before) then they're probably stuffty at most, if not all, levels
for example, pichu in melee. basically if you're putting any sort of energy into your play and you're not like an 8 year old, you can beat people that play pichu. unless they practice a forgetton, you can beat pichu.
the same logic applies here. this person isn't extremely practiced and dominating with mii gunner, they're playing at an average/above average level. with the right characters most people at the same level should be able to beat them without making a "chore" out of it