I know exactly what he means. If you've really played on a truly incredible vintage Fender 4 string you'll know. I can't describe the physics, on a 5 it somehow compresses & evens out the sound. It takes that extra special something away from the money zone on the E and spreads it over the bottom 2 strings. That extra mass in the neck must have something to do with it. I've noticed this with all the best 5's I've owned (MTD 535, Stingray & my current main bass, a Celinder update). It's particularly evident with double basses, I've never played a 5 string with a good E. The 4 string with C extension rules in that area. I'm not saying there aren't exceptions to this but it seems to be a general trend.
Will it stop me playing 5's? No.