.... I am sure it's very good, just as Canon and Nikon weather sealing is very good but does it exceed the international IPX1 certified standard? < No it doesn't. The IPX1 certificate awarded to Olympus is claimed as a camera-world first.
Do I value it? < Yes I most definitely do. I am outdoors in all weathers often from dawn til dusk and
I want the peace of mind which the Pro Olympus system offers - I have missed shots due to faffing around under rain covers before now.
For anyone new here who hasn't seen it and there are other videos showing performance in extreme sports environments :
View: https://www.youtube.com/watch?time_continue=36&v=5jpgsXzgXVU
.... Yes the lenses are "compatible" in that they can be easily mounted, are not reverse engineered, and most features are functional, but not all. For example, the Olympus Pro lens's customisable L-Fn button on other bodies. Another example are the Pro TCs only fitting Pro lenses and other m4/3 TCs not fitting Olympus Pro lenses. It is a loose agreement and not coordinated in feature details and electronic communication and I think that as technical advances are made, the brand differences will continue to widen - They have to if only to give brand marketing advantages. The parties to the M4/3 agreement are separate independent companies.
If you want evidence of this now, just contact technical support and ask for some help or advice which concerns your lens><body when you have mixed brands even within the m4/3 agreement - It's merely an agreement and not an overall technical system which is coordinated.
Yes, I am biassed towards what works for me both physically and very importantly gives me peace of mind. When you pay about £2grand plus for a camera body why would you mount anything other than the highest spec lenses you can buy which are
very specifically designed for them? < It's up to you of course but when I'm asked what I would do or advise then I offer my advice - It's entirely up to the reader whether they take notice or not. I don't have to offer any advice at all but I am given advice and so like to give back.