I think the suckless project has correctly identified that a lot of software sucks, but their attempts to make it "suck less" are focusing on the wrong points. A lot of mainstream software is grossly inefficient, bloated and resource-intensive, and that's not necessarily because they're featureful. It's certainly possible to write software that is both featureful and efficient, but suckless aggressively cuts features instead of optimising, to reduce the perception of inefficiency; what's left is not necessarily efficient.

In fact, I don't remember the details now but I recall looking at the source for another one of the suckless applications and finding some pretty inefficient algorithms. I think the other comment here about st being CPU-intensive with high output rates is an example of this.

Ironically, one of the reasons I think mainstream software sucks is because newer versions also tend to remove configurability and features often for the same goal of reducing bloat.