I'm in the Top 50 and play against the highest ranked players in the game. I have some concerns about the scaling of unit levels at the higher levels. As levels on units get higher and higher, the relative difference in power per level seems to get more noticeable. The handful of times I've encountered players with level 9 units, those units had a distinct advantage against level 8. This creates some really frustrating imbalances when the units in question are the kind with a slow rate of fire but high damage. A few examples where level variance has an outsize effect on gameplay are things like:
GDI Talon needing 4 hits from a lower level Talon, but killing lower level with 3 hits. This is enough of an imbalance that it more than negates defensive advantage because Talons fire so slowly. It goes, You hit, I hit, You hit, I hit, You hit (my talon survives with a sliver of life), I hit (yours dies). And now my surviving Talon will guaranteed get a shot off when you come to fight, and I'll do 1/3rd damage to your Talon before it finishes me. In practice this means each of my talons is like 167% of your talons, because of a slight level difference. Unreal.
The interaction between Stealth Tanks and Pitbulls is also out of whack with levels, given the Stealth Tank has a massive delay between salvos. A level difference is the difference between if my Stealth Tank can kill a Pitbull in a single volley, or leaves the Pitbull slightly alive, at which point the Pitbull can kill the Stealth Tank before it can reload.
As the game continues this gets more an more frustrating. It's not really that rewarding of a feeling if I smash somebody because I know how to abuse a level difference I have over them - I want to win because I outplay them, not because my same-cost unit is 150% more effective than theirs.