For what it's worth, I had been using m43 for over 4 years until I switched back to Canon, this time it was FF - 6d. It's been nearly two yeas and I never once looked back. The IQ, color response, tonality, noise, etc. have been a quantum leap from E-M10 and E-M1.
The most important discovery for me was that I shoot with 6d+24-70ii 99% of the time. The convinicence of a single lens combo and seeminngly endless battery life - well over 1000 shots, much improved ergonomics over Olympus system; for me, far outweighs the lighter weight/size of m43 and multiple lenses, constatly changing. I could never effectively use 12-40 lens for portraits, not nearly enough DoF control. Had to always switch to 45mm 1.8 or 25 f1.4, changing and charging multiple batteries, unreliable AF in low light, etc.
I think if DoF control, portraiture, speed (sports, running kids), postprocessing lattitude, large format prints, etc. are not important to you, then, yes m43 is lightweight stystem for the rest. For street and, perharbs, travel photography - m43 is more than adequate.
However, I was frequently stuck with just PL25 (back in m43 days) for its light gathering and rendering properties. Switching to 24-70ii made my photography so much more diverse, all kinds of prospectives in one session w/o changing lenses. And files can take a lot of abuse in LR. I am so looking forward to the 6dii with its DPAF. To be clear, I always have my RX100 (iii) with me which is used for video and casual restaurant shots with its bounceable flash.
These days I tend to think that Fuji has developed the most well rounded mirrorless system.