I think there are two issues. One is that if you are trying to get Olympus TTL from an LED that will I think be very difficult. 2 mm single core fiber most likely will have a very low NA so that might not work well. For less than 20 euro you can test out using a double fiber setup using the Inon Bushings and some 1 mm single core fiber (I can send you a double fiber cable if you want). The multicore fiber is about 6 euro per meter. No one you dive with has some good fibers?
I don't have the SWAL but the tests from Bluewater suggest that it will vignette a bit on the EM-10. I am sure that you can find a zoom setting where vignetting is not appreciable, but for a micro 4/3 sensor it will probably not be as wide as it will be on a compact sensor. as for the WACP, it probably won't work very well except on full frame cameras. BUT the results that I have seen from that lens are quite nice (a bit pricey though).
TTL exposure underwater can not be better than TTL exposure of the camera/strobe on land. In my hands at least, Olympus EM1 mark I had pretty poor performance of TTL using the small flash at anything other than f5.6 to f14. Outside those bounds, I got very uneven results. Certainly fiber optics can play a part, but it is hard to understand how two shots 5 seconds apart could yield one over and one under exposure with the same setup.
Get the Nauticam version, for sure it will work with EM-10 (for the right lens). To the OP, I guess that what you want (small camera, completely versatile on a single dive and quality of DSLR) is very unlikely. I shoot the EM1-II and like it a lot, but it is not quite the same quality of a DSLR. Also, when you think of wet lenses, they are never quite as good as a prime lens in the appropriate port.