i think you're getting things a little confused.
From what you've put, you get full speed when both wired to the modem and when wired to the orbi. Actually getting over what you're provisioned. Is this correct?
You're wireless is variable. Some devices getting 100mbps and some getting 400+mbps from what you've wrote prior. this is probably going to be how it is. orbi dynamically moved devices between 2.4ghz and 5ghz as well as each device has its own wireless specs. If you're testing on a phone that only uses a 1x1 antenna, its going to be slower than a laptop/phone that uses a 2x2 anteanna. As well as if the device happens to be connected to 2.4ghz radio when you're speed testing, its going to be significantly slower than when its connected to 5ghz. This is the very nature of how bandsteering works. As devices repeatedly need more bandwidth, the orbi learns to place them on the 5ghz band if they're close enough. A test or 2 isn't going to get them to connect to 5ghz in my understanding.
You also have to take into account home environment. If the 2.4ghz is more congested, its going to be even slower than if you lived in the country. Or if your home has walls with plaster lathe, foil lined insulation, brick, concrete, etc.
Another thing to keep in mind. Orbi isn't goign to be faster than a R7800. A flagship router is going to be faster than orbi but orbi is going to be more consistant and have better coverage because of its satellites with wired/wireless backhaul.
