This is probably the most theme-appropriate thing that could have been done, and it's a pretty good implementation of it too.
The "Increase maximum of both convex and concave lenses by 5" upgrade only increases the maximum of convex lenses by 1, which makes the lategame harder than it would have been because convex lenses are pretty important. (It does increase concave lenses properly, but those are less useful given the game is all about focusing light on a point.)