Using Google DNS as an ISP

For a while at the WISP I work at we have been casually programming 8.8.8.8 and 8.8.4.4 as static DNS entries into the equipment (customers routers and CPEs). I have always felt that as the ISP we should be maintaining our own dedicated DNS servers, but Google seems to work fine. Recently, a change was made to all equipment on our network to have all the backhauls, AP's and infrastructure use 8.8.8.8 and 8.8.4.4

This to me seems wrong (as I have indicated), but I don't know enough to prove my case. I believe based on search results and product forums that Google DNS rate limits quereies to 100 per second. When I torch the fiber interface at the main gateway of our network, it only evershows 90-105 connections open. I have a feeling that the rest of the quereies get dropped. Is there any way to definitively prove my theory?

I know enough about networking, but to be honest when working for an ISP at this scale, I usually just trust my boss. Recently there have been massive, random unexplained issues with peoples connections (aside from normal congestions and network conditions.)

Our ISP network is set up as such that there is 1 gateway that divides the connection between ~44 towers, each tower has its own public static IP that is bridged back to this main gateway. However prior to this change the 200+ backhaul devices were using our local gateway at 10.0.0.10.