I'm assuming all of your access points are wireless and are communicating via mesh? They are NOT wired backhaul access points?
Also, what version of Google Nest Wifi are you using, Pro or V2/V1?
Ultimately, the speeds you are seeing are reasonable based on how mesh works. It's very counterintuitive and based on the signal you're using, 5Ghz vs. 6Ghz. That said, if your access points do NOT have direct line of sight to your main router point, the speeds you describe seem correct to me. And by direct line of sight, I mean that literally in that if when you place the access point in whatever location you deem and can't see the router, the signal will be degraded significantly.
Google Nest Wifi communicates wirelessly with it's Access points over 5Ghz and this is actually the same channel that wireless devices communicate over (along with 2.4Ghz), so you can see that this gets complicated quickly. It should be noted also that the further the distance the access points are to the main router means that the wireless access points need to work harder to establish and talk with the main router. Sadly, you could join one of those access points, see a great signal and an hour later it could be weak and your wifi is grounding to a literal halt.
Mesh doesn't really work the way many people think, in that, each of the pucks piggyback each other and everyone talks nicely to one another. No, that's NOT how it works. Every access point will want to talk to the main router and they will do everything in their power to complete that connection. As the distance increases or the building materials block signal, your wireless mesh experience will become intolerable. You might restart the access point or router and then miraculously everything is working again only to become unstable an hour later as the access points struggle to get a good signal to the main router. This is the part where you go insane and believe me, I've done this madness for you. I know it sounds absolutely counterintuitive to "wire" something that is essentially designed to work wirelessly. However, after really understanding how the mesh standard works and how that standard was implemented by Google, it now makes much more sense to me. But, again, I get the first impression of "this guy is telling me to wire everything, why? shouldn't this all work great wirelessly and isn't that the whole point?". Yea... no.
I spent literally hundreds of hours trying to solve this problem, reddit posts, google nest forum posts, chatting with experts and non-experts alike. I would position access points, try various hacks and ultimately I gave up and decided to wire everything (it wasn't too bad cost wise, I had a friend help me).
Backhauling is the jedi mind trick to solve every wireless mesh problem.
In wiring everything, meaning, I run Ethernet to all the points (via unmanaged switches). I'm running the Google Nest Wifi V2 router pucks (AC2200). I love them now. They provide excellent wireless coverage through my entire house, but they are ALL wired, not a single point is communicating with the main home router wirelessly.
When I started this insanity, I had ONE main Nest Router (with ports) and 4 Google Nest Wifi access points (the speaker pucks with NO ports). I returned every single Google Nest Wifi access point (the speaker pucks) and replaced them with Google Nest Wifi Routers that do have ethernet ports.
Once I wired everything, my wireless speeds throughout my house are 200-300 mbs.
Again, I have a somewhat complicated setup and my house has a separate structure, courtyard and very dense building materials (stucco, brick, wood cross braces, etc) that wreck wifi signals. I just realized that running a wifi network via wireless mesh was NOT a good option for my house and setup. I wanted reliable/fast signal and wiring the system was the only way to do this. I'll end with this, you may think this is a Google specific issue and you'd be wrong. I was so fed up with the performance and reliability problems I went out and purchased some Amazon eero 6E's and attempted to get it all to work better. It was worse. Why? well 6Ghz has even more problems with distance and signal interference and the performance was actually worse than the Google AC2200 system I had setup originally.
Good luck.
