sorry I don’t know E-5.
> You’re comparing the size and weight of a Canon f/4 lens to an Olympus f/2 lens.
28-70/2.8 (old versions from Canon and Nikon) can gather one stop more light than 14-35/2 and you can see this in the output image in one stop better SNR (shot noise) or +3dB at open and same shutter speed. the difference may not be exactly 3dB but that error comes mostly from sensor.
14-35/2 can do same as, better at corners than, 24-70/4
35-100/2 can do same as, worse resolution than, 70-200/4
neither of them AF well compared with Canon/Nikon lenses.
70-200/4 worths less than a grand, 24-70/4 should be cheaper, maybe about the same with IS. I’d like to value 14-35/2 more than 24-70/4 for quality at corners, then adjust it down for narrower zoom range (24mm and 28mm are very different). 35-100/2 should worth no more than 70-200/4. there is nothing more we can expect to get out from the lens.
Started out doing photography at the age of 6 using an uncle's old 1940 kodak brownie box camera. At 15 years of age, I decided to buy my very own 1975 Praktica SLR camera. I now shoot with a Nikon D850. I do unpaid TFP and commercial paid work.