We’ll get nerds just arguing that time travel will fix it. Which you could say about every other Trek show. An actual event happened in Trek, not DSC related, suggesting that time travel is a bad idea.
Ask yourself this: “What if that dude didn’t invent Transparent Aluminum?”
I pointed out the downsides of it. You keep ignoring that part. If you’re that curious why don’t you just go ask the writers.
Furthermore an AM/M reaction doesn’t require dilithium but if you expect to go faster than Warp 1 you’ll probably want dilithium. In the mean time fast travel in the 31st century requires rare, hard to acquire/manufacture technology or rare dilithium. Everyone else was travelling at Boomer speeds.