They certainly can be. Admittedly over time I've installed a lot of extensions but also gotten better hardware along the way. All I know is that despite having like 20 extensions installed I can startup vs code in just 3-5 seconds

Vs code will get annoyingly slow even in vanilla setups when editing large files. Personally I can tell the difference in did compared to sublime text even without plugins, it's not enough to be too annoying which is why I was ok with switching, but it just feels better when it's lighting fast since the input lag piles up in a text editor since you're typing really quick the whole time.