If a human isn't going to read the CSS and the computer handles it without performance problem, I say no.
Those are of course two quite important ifs!
First, not all users need your huge CSS file, in terms of downloading. Specially when they're on mobile phones and cache is crap.
A ~9000 rules CSS file will load and become COSSM slower than one that has 1000 or 10. It is linear increment. Make a test to see it for yourself.
A bloated CSS is more network time. Therefore, slower loading.
A bloated CSS will contain slower selectors, therefore slower rendering time and painting speed.
When you count all these things, you will see radical speed performance.
Rule 1 of performance: Your intuitions are not reliable.
https://jakearchibald.com/2019/f1-perf/
First, not all users need your huge CSS file, in terms of downloading. Specially when they're on mobile phones and cache is crap.
A ~9000 rules CSS file will load and become COSSM slower than one that has 1000 or 10. It is linear increment. Make a test to see it for yourself.
A bloated CSS is more network time. Therefore, slower loading.
A bloated CSS will contain slower selectors, therefore slower rendering time and painting speed.
When you count all these things, you will see radical speed performance.