Yeah the fact the frequency and speed of asteroids follow a linear curve seem to make it so the start is rather dull and things spike into chaos.
I'll admit that the various perks for the signs are probably just way too overpowered combined with the fact they always heal you to full health means if you get a bunch of Cancer signs you can just have so much max health and shields that you just can't die, and the way resistance is set up is also way too strong and means you also barely take any damage with the right streak of signs
Not sure what happened with the whole disappearing from the screen, the border "walls" aren't really thin so unless you got a REALLY high amount of speed, glitching out of bounds shouldn't be that easy but i also don't see another reason, so it's probably that