EQ is never "worse than nothing".

??!! Never? I beg to differ. I would say EQ is almost always worse than
nothing, & maybe rarely slightly better than nothing in cases where the
room has been sorted out acoustically already.

But if the room has bad acoustics, the
improvements EQ effects are minor and not worth the trouble. (Yes, I've

applied EQ in bad rooms, both in homes and businesses, and it
pointless.)

Agreed.

By the way, detailed digital EQ can also correct errors in the
speaker.

Yes, where the speaker is demonstrably deficient in anechoic tests, EQ
can correct this such that the output into the room in question at
least starts out flat. After it gets into the room, though, the EQ is
no longer a useful part of the equation.

Scott Fraser