That lens is a bit tricky to judge. It is a 300/4, but it's use case is not the same as a 300/4 on FF camera. It's a poor man's 600mm. As far as I know, the only "budget" option to get that reach at good quality is a Canon crop DSLR + 400/5.6L. It's not exactly equivalent, but pretty close. So it doesn't look like there's much competition at that price point. I guess cropping is another option, but only until most MFT cameras are 20 megapixels and more.
I guess if you think of it as a 600 f4, its a bargain.
But it's not a 600/4. And in many situations can't replace one. It does however give you that field of view. Something that costs a pretty penny if you want/need high quality. If you're into equivalence, think of it as a 600/8 that's 1/5th of the price of a 600/4. Not a bad deal if you can live with f/8. Not that FF shooters have this option (again, unless you can live with lower quality).
But I prefer to pay for actual materials and labour
It doesn't work that way. No company will sell you their stuff for the cost of materials and labour. At least no company that wants to turn a profit. And do you think the R&D and prototyping stage is free? I bet by the time everything is ready for production, the project already cost Olympus couple of million bucks.
and see no reason it should more expensive than equivalent lenses from other manufacturers.
By equivalent, do you mean with similar optical properties, like the 300/4 from other makers? Or completely different lenses that would offer similar things in their respective formats (so 600mm for FF, ~400mm for APS-C, or other combinations to get the similar end result)?
The new 300/4 from Nikon is 2000 EUR, so why is Olympus introducing their 300/4 for the same or lower price such a huge deal? Why do you think that such a lens introduced in 2015 should cost the same as a lens that was introduced almost 20 years ago? And we don't even know how it performs. For all we know, it might wipe the floor with both the more expensive Nikkor and the ancient Canon alike. If it turns out like that, why do you think that extra image quality is not worth any money?
Here were Olympus has to put up or shut up. If they want to attract the professional market, they have to take on the competition on their own ground.
You mean they should have announced 300mm f/2 for $10,000?
I understand Canon looses money on the big whites (well some of them)
Really? I would be quite surprised if that were the case. Apart maybe one of those monsters that they made just a few of or something.
and possibly some other specialist lenses as well
That might be the case with some very niche specialty lenses. The most famous story is about their tilt-shift lenses. But I would not be surprised if Canon recouped their costs after all those years.
but that's accepted as the price of capturing the pro market. I assume its the same for Nikon.
I don't think this is the same level we're dealing with here. This Oly is rumored to be sub 2000 lens. It's not a $15k monster that only big organizations can afford.
Most pros have to work to tight margins - cost is an important factor, probably more so than many enthusiasts - (except for the elite few who can charge what they want).
Again, we're talking sub 2000 here. Less than any pro-grade FF body. Less than a lot of pro-grade FF lenses.
While an adapted lens may not be as good, when the money for glass gets serious, another very real option is to buy a different body. So the Canon (or Nikon) lens option could lead to people going back to DSLRs to do the job.
That's kinda backwards. If you're shooting tele for your job, you're not using MFT anyways, as there are no pro-grade options in the system. And if you're shooting MFT professionally and need a tele for a one-off assignment, than you just rent a gear needed to do it. And if you're shooting MFT and you need to start using telephoto lenses more often, you simply have to switch to a DSLR, as there are no pro-grade telephoto glass for MFT (notice I'm ignoring 4/3 lenses here).
But where your argument fails is the economic calculation. Why do you think spending $2000 for a Nikon body and a 300/4 lens is more cost effective than spending $2000 on a lens for your existing system? What kinda argument is that? And let's just ignore the hassle of cropping your shots, as that's something you'll probably do anyways. Or the fact that the cheaper Nikkor 300mm is not exactly a stellar performer from what I heard.