Really, any speed settings would help make the game more accessible and approachable.
Some people may enjoy the parkour elements but not have the motor skills to handle high-speed reactions.
Other folks may be great at the fast paced movement, but get frustrated by the number of enemies or the speed of projectiles.
If you are able to offer sliders (or even just low/medium/high) options for things like movement speed, enemy frequency, damage taken, and grid reaction time? If you can do that without having to remake your code or game engine? It'll mean a much wider potential audience for your game.
Speedrunners and streamers can have fun setting everything to the fastest and hardest difficulties. Casual players can have fun with it without getting frustrated.
And sweet, you've got a Linux build. I do most of my gaming on Linux now. I'll try to check out the demo.