I am not sure it bottlenecks it to any great degree, judging by this video:
https://www.youtube.com/watch?v=9Vgx5Ub9qgU
Which has the 2080 ti in 4 different set ups I5 8400 vs I7 8700K vs I7 8700 vs I5 8600K, and the framerate difference is pretty small. Like 10 FPS at 1440p ultra settings in most of the games.
Compared to 2080 ti and an i9 9900k, in Shadow of the Tomb Raider, 130 fps, i5 8600k 113 fps in that video at ultra.
Yes it is less, yes you would get more out of a better CPU, but not a great deal more - given the amount you might need to spent. I mean 27 fps isn't that huge.
