That's definitely a valid point! That said I'd argue that you can also adapt EF glass to Sony cameras for a similar price, though admittedly I doubt the performance would be quite as seamless as it'll likely be for the EOS-R.
Moreover there are more and more options out there for the E-mount at a reasonable price, so long as you're content with not immediately aiming for the G Master line. The new Tamron 28-70mm f2.8, for example, is apparently a great and relatively cost effective option for a quality all-rounder zoom lens on that mount. And if you're cool with shooting in Super35 mode a bit more often at first, Sigma has a few E-mount primes for APS-C sensors that are pretty affordable too that I hear are great.
And by the same token, the most exciting part of the EOS-R right, I think, is probably the new EF-R line of lenses... which are similarly pricey to the Sony G Masters.