Imagine having access to Houndoom during the midgame, one of the greatest in-game mons of all time, a mon that is so good that it had to be removed in PLA to encourage people to use Hisuian Arcanine, but still complain about fire types.
Fuck it, let's look at availability in Johto and Hoenn, two regions no one complains about fire types in:
>Johto
Growlithe
Vulpix
Flareon
Magby/Magmar
Entei
Vulpix is exclusive to Silver, Magmar doesn't appear in Crystal, and Magby must be hatched from the odd egg. Entei is a roaming legend and requires you to grind money or coins for a fire move that's stronger than ember. GSC Flareon is....awful. For most people in Crystal, Growlithe is the only option. Ponyta doesn't count because it's not found until you set foot into Kanto
>Hoenn
Slugma
Numel
Torkoal
Vulpix
Better selection on the surface, but no one ever picks Slugma (don't lie, the five people who used Slugma only did so for the sake of being that guy who used it) because it's one of the worst pokemon of all time and Vulpix is found so late that most people have already finished their teams by then. It's a shame it's so overlooked when you get the sunny day TM right before catching it. While not as good as Growlithe and Houndoom, Numel and Torkoal are still quite solid. Castform is a meme
Now we look at Platinum. Rapidash is okay as usual, Houndoom is an elite fire type, and Magmar is still great even without evolving since it has good mixed stats without sacrificing speed and can learn thunder punch. Even Flareon, while not very good, is still much better than in gen 2 and FRLG since you can teach it flametheower without any issues. This is not a bad lineup. It's not as good as RBY's selection or BW2's bloatfest, but you're given an okay option, a great option, a god tier option, and the flamethrower TM without any issues in Platinum.