I honestly don't think I can directly hear the effect of waveguide. Assuming you're not calling large studio monitors "main", you'll find many top players still rely on old NS10M, 1031, ProAc, etc. You may want to check MIX magazine or manufacture's web site to see who uses what monitors these days. I do not follow the most recent trend, but last time I researched, it seemed ATC was gaining popularity along with Amphion and Barefoot. I'm sure they are all capable mixing monitors, waveguide or not.
A simple definition of a wave guide and a horn. A horn is to direct sound and make it louder. When you direct the sound towards a given direction it will be louder, like cupping your hands around your mouth and calling for your kid to come home for dinner.
A waveguide is about matching the dispersion between two drivers at their crossover frequency, so the speaker disperses uniformly. If you don't have a waveguide a speaker may sound good directly but not to the sides. In most two may monitors it matches the tweeter's dispersion with the woofer's dispersion at their crossover frequency.
The waveguide doesn't change the direct sound much if listening in the prime spot and at close distances where you don't hear many reflections compared to the direct sound. You will notice waveguides do better when you are not in the prime listening spot or when listening further away where you the reflections in the room get mixed more with the direct sound.