This thing is so damn popular and I have literally no idea why past just "Nostalgia".
I have pretty much the same reasoning for hating Meganium too but Typhlosion actually has fans so I'm going to get right onto it.
Typhlosion is just so damn BORING.
Typhlosion is literally Charizard without wings and a worse movepool. I realize they're going for something that eases the gen 1 players in, but it has nothing good about it to differentiate itself other than Eruption. It's design is bland as hell, you'll struggle to find a good move in it's pool that isn't fire or normal... it's at least a good special attacker throughout the game, but at the end of the day, why would you want to use this over something like Charizard or Arcanine or Houndoom? I can at least see why Charizard is popular besides just nostalgia - it's a Dragon, it has a defined change and design, it's very usable and reliable in-game, and it even has a somewhat interesting movepool including Flying and Dragon moves. Fine. Typhlosion... is sort of decent in-game, it goes through practically no change since it's base form other than "bigger and opens eyes", it's design is so boring and bland rather than badass, and it even has THE EXACT SAME BASE STAT VALUES as Charizard - in the end it just looks so inferior to Charizard I just can't find myself liking it at all.
I adore Feraligatr so much. It's easily the saving grace of the Johto starters to me, because there's nothing else to look for in that area. it goes through changes, it has a defined design, it has a great and unique movepool, an interesting stat spread and a very different role from most water-types - and it's very difficult to stand out in such a populated crowd as that. But Typhlosion fails to stand out or do anything different in any way, and that is why I cannot find myself liking it at all.