Terraria is quite a lot of RNG, and there are some things you cant control or decide. You don't decide when you want your NPC's to come, you don't decide when a slime spawns, you cant control where the floating islands are when you spawn,You cant control what you find in a chest, and a whole lot more other non choices.
But, you're not complaining about where shadow chests are in the underworld, or which side the dungeon is in, or where are caves in the underground snow biome. I'm not sure how this idea came to mind because you were trying to find platinum, but removing a biome from the game is hard. Especially crimson. Removing big parts of the game can make gamers upset. And last but not least, In crimson there are vampire knives, which you dont like according to your post. If you do like them, then pick one, remove crimson, make gamers upset, remove vamp knives, or keep crimson keep vamp knives, an keep alot of gamers happy.
In conclusion, Crimson needs to stay. Once a biome always a biome.