Oh yeah there are definitely brushes out there, equal to or better than those by MAC at all sorts of varying costs. But for me comparing my full size, full price MAC brushes to those in the MAC brush sets I do see a big difference. I'm just comparing the MAC ones here though, not anything else. I've heard quite a few other people say it too that the quality of the SE brushes is just not there.
For example my 239 full size has great colour pick up, fantastic for packing on eyeshadow and pigment. Whereas the 239 SE is terrible, made of totally different material, picks up hardly any eyeshadow and I've now relegated it for application of paint pots only.
I just think the set I got wasn't worth the £39/almost $80 I paid.