Just don't talk to the people who want super wide angle lenses (easier to do with a larger sensor)

Olympus has a well-regarded 7-14mm rectilinear lens. The widest non-fisheye for APS-size sensors (Canon, Nikon...) starts at 10mm, which gives a bit narrower view than the Olympus lens. The widest rectilinear lenses for 35mm film/sensor start at 12mm, a bit wider than the Olympus lens, but there are only two choices, the Sigma 12-24mm (terrible corner sharpness and the usual Sigma quality control), and the 12mm Voigtländer Heliar, which is only available for rangefinders. I think Olympus has their bases well covered (that is, apart from the lack of primes and fast lenses).

What limits wideangle lenses is not sensor size (how many ultrawides do you see for medium format?), but the mirror box. The closer you can place the lens to the sensor, the more symmetrical (and smaller and well-corrected) you can make the lens (compare Biogons and Distagons). Making an excellent retrofocal ultrawide lens is a damn hard job.

(I'm not an Olympus apologist, I use the right tool for the right job.)