No, the Sattellite service should havce no impact on reported MESH speed.
Is this on a "metal" [marine] vessel? You might be fighting with a lot of reflections.
Perhaps other things are using up some of the airtime. Check out Wireless/RF Spectrum to see how much is free. You could also click on the MR84 on that screen to see how the individual channels are. The MR52, being a repeater, doesn't have much choice in the issue. It needs to use the same channel as the MR84.
If you change the antenna on the MR84 to a focsed antenna rather than using an omni you are almost certainly likely to get a better speed.
You could also consider devoting a particular band (such as 5Ghz) to the MESH backhaul and leaving 2.4Ghz for the clients. Check out this article:
https://documentation.meraki.com/MR/WiFi_Basics_and_Best_Practices/Wireless_Mesh_Networking#How_does...