The main difference is that MoCA is designed to run over coaxial cable, and G.hn is meant for use over power lines.

They have similar use cases ("route data over wires that already exist in your homes"), but different problems (MoCA: avoid interfering with your cable/satellite/cable modem feed, G.hn: deal with the absolutely abysmal signal quality on power lines, avoid accidentally broadcasting in the FM bands,...)

From a modulation perspective, G.hn wave 2 and MoCA 2.0 are broadly similar. They both use OFDM as the main modulation and LDPC as the FEC. They both are scheduled networks (like 802.11, unlike wired ethernet) where a master node allocates transmission time slots to other nodes. The devil is in the details though and I'm not as familiar with the G.hn wave2 spec as MoCA, so the detail I can give you is limited.

You alluded to it but the other difference is MoCA is shielded, EoP turns your house wires into a ton of radiating antennas across the frequency bands. I still have no idea how the FCC even approved the damn things after seeing what they do to the RF spectrum nearby.

Correct. Coax is nice and quiet in both directions. In home power wiring is basically a giant, poorly tuned antenna.

I can tell you MOCA 1.0 can be made to work over powerline (at reduced bandwidth, if you rip out the RF frontend and run at baseband), and it can pass emissions, but it didn't work well enough (by % of households able to achieve >= target data rate) to be worth commercializing.