GBBR have a role and a realism aspect, but a well tuned AEG will be beat them in every way. Except in super heavy rain, where electrics do not fair very well.
GBBR's have a cool realism aspect you will not get on all but the very highest end GBLS M4. Which cost around 3-4 times more than an MWS. Even then, the GBBR has the realism edge and a nicer trigger.
But you will have to deal with gas temps, purging mags, higher maintenance and much lower ammo counts. All while carrying mags, which weigh a lot more and are relatively fragile compared to an AEG Midcap.
I am still yet to be won over by my MWS, which I hope will happen by turning it into a 1.88J DMR running 0.45s
I want to love it, but i would rather win