I'd say they're a lot less useful than our card rankings. With cards, often going for the power cards when there's no great combo and no good counter when your opponents don't will lead to a win, even if your opponent is someone considerably better than you. Tier lists only matter if skill is incredibly close, and even then, it's the actual matchup between characters that really matters - tiers are just a generalisation of those (for the most part), and even then, tiers only matter at the metagame level of play, and even then, they have less of an impact than luck does in many cases.
In other words, tier lists for Smash Bros. are irrelevant to 99% of people.
Yet 1% of the players seem to control 99% of the opinions. Occupy Tier List!