Depends on the game and the skill level of the competition. Tier lists assume competitive players who understand the metagame. Some characters are going to inevitably be better than others because their moves have higher priority, their moves happen faster, the character is faster, the character has a smaller hurtbox or bigger hitbox, their combos are better, they have access to unique mechanics which favor them, their playstyle lends itself well to the game's mechanics, or their moves are just easier to execute. So there are inevitably innate differences in quality between characters. There's also match-ups, due to the interraction of two competing optimal playstyles one character who is bad in most other aspects may do favorably when matched up against a character that more conventional (metagame dominant) playstyles struggle with. Match-ups will be accounted for to some extent in a tier list, but it won't be controlling so if you just go by the tier list, you might be in for a rude awakening against a skilled low-tier player.
So to answer your question, tier lists give a decent understanding of how characters qualities compare but it is only a heuristic outside of competitive play. Things shape tier lists that do not affect casual play, but the most controlling factors (relative quality of the characters) likely will. I'd recommend further reading on the strengths or weaknesses of a character if you want to know how they'll actually stack up against totally random opponents.