If you are getting gamma shift and you have used your scopes to keep it in the Rec.709 Color space (16-235) The most likely problem is color correction on a un-calibrated monitor usually in full color (0-255) and gamma of 1.8 (default on Mac)
Whether using restricted or full range for monitoring / scopes doesn't matter as long as the display chain in Resolve is expecting full or restricted, could be limited RGB over DVI/SDI/hdmi or 4:2:2 or 4:4:4 as long as the display can handle and capable of excepting that signal. Quite acceptable and preferred by many to monitor full range, as long as when encoding for final output limited range encoding is chosen in Resolve's delivery tab. Or full range if going to an intermediate. So full range RGB on a mac is no problem if that's the default for an Apple display.
Gamma is 2.2 default for me on Mavericks not 1.8 and I've not been in messing with those settings it's worthless.
Now if you have adjusted your display with a colorimeter or at least with the Mac Monitor calibrated software
1. Get the display into a acceptable state (as close to 709 standard as possible) for profiling and 3D view LUT creation by using the displays hardware controls, if the display doesn't have decent controls it could well be limited for calibration if it's drifting, just useful for GUI.
2. Ensure no ICC profiles are interfering with the display's gamma. Difficult to kill on a mac.
EVZML is using Resolve so:
3. Use a probe (i1DisplayPro) and suitable calibration software (hcfr to report, DispcalGUI to profile/LUT) to control the Patch Generator in Resolve, probe checks patches from within Resolve GUI or preferably patches on an external display fed by a Blackmagic Mini Monitor to bypass any levels scaling through the vidcard interfaces, DVI, hdmi, DP.
4. Build a 3D LUT for monitor based on rec709, D65 & BT1886 gamma with 2.4 power curve.
5. Put 3D LUT (.cube) in Resolves 3D Monitor LUT slot and set Viewer LUT to Monitor LUT.
Now have calibrated monitor and colour managed app. Resolve doesn't use ICC profiles so all that is redundant including OSX's calibration by eye guff.
Then turn off Automatic gamma adjustment in the ProRes Codec option , I assume your intermediate mov is ProRes .
I use Apple compressor for all my H264 and never had a gamma problem between PC & Mac , it's the same h264 I upload to Vimeo & YouTube.
Resolve's QT h264 output on the mac is incorrect, Windows isn't. But one thing I agree with you is that going to an intermediate codec and then encoding h264 etc from that is better route. Me I use x264 and apps like Handbrake for that.
Web, Vimeo & Youtube output through a browser on a PC or mac I wouldn't judge anything on personally.