It makes sense to classify villagers by species, especially when making a guide. It also makes a lot of sense to classify them by personality. But to classify them by popularity, that's ridiculous. It's okay to classify them by popularity on the forums only to suggest what the best minimum bids and best buyout prices are. For example, when a villager isn't popular enough, they would suggest giving away for free, whereas the more popular a villager is, the higher the pricing should be. It wasn't meant for multiple discussions like the opinion threads or describing them.
What's even worse about the Tier System is that people take it too seriously. Like when a Tier One villager is moving, the person would time travel back multiple times to hold them for sale as people who want him/her would fight over him/her. Another example is how some dream towns get a very bad grade for having villagers that aren't popular enough. They'll even get as offensive as South Park if you have only one Tier 5 villager.
The tier system was to show which villagers are popular and which villagers are not, as well as suggest what's best for trading deals. Now it's a system that people would use to bully others (including unpopular animals). So I'm okay with the system, I'm just not okay with the obsession over the system.