If the CPU can prepare and send more than enough draw calls to the GPU to keep it constantly busy, then the game is GPU bottlenecked. It's quite conceivable that a 10900K operating at roughly 5ghz would easily keep a 2080Ti GPU bottlenecked at 1080p high settings in Dota 2.
For comparison, a high FPS game like Doom Eternal at 1080p still received a large 40% performance boost when going from a 2080 Ti to a 3090, and on a
3900xt platform no less, indicating that the game was still GPU bottlenecked at 1080p and this game has one of the best implementations of Vulkan out there:
Custom-Designs der GeForce RTX 3090 im Test: Benchmarks in Full HD und WQHD (Update) - ComputerBase
For practical purposes I agree, but when performing a CPU performance test, the resolution should be set to 720p or less to minimize GPU interference.