It's oddly satisfying gradually become so powerful that everything just kind of dies when you breath on it. I liked the enemy spawn rate early on it felt pretty well balanced if you were trying to play more greedy.
One issue with giving every enemy chase AI is that you'll notice that they bunch up a lot and then the player will gravitate towards circle strafing that blob of enemies. One way to help mitigate this without having to introduce more enemy types is to give the enemies some push away factor from each other so they're less inclined to bunch up so heavily. You can look up boid flocking for a relatively simple way to introduce some spread.
I'd also maybe tone down the offensive upgrades since bullet count and penetration are basically stacking multipliers to your damage and can easily snowball the player DPS.