Houston you have a problem, with that said, your speeds are plenty fast. But you're not getting what you pay for by any means..
1. Have you tried different devices to do the speed test?
2. How about testing with a up to date cell phone?
3. Have you tried selecting a few different speed test sites? A simple search will turn up many.
We pay for 300 Mbps fiber service @ $57 a month actual payment.
I LOVE my wireless router, even though it is dated in the router world as it is an "N" router. The range is fantastic (I've been computing since 1995) router still in production and rock solid all the time. Since I "only" have 300 Mbps service and this router claims its good up to a gig I dont need the latest router classification, all I need is the great range and I got it, as well as rock solid performance.
After seeing your post I ran a quick test/ from my couple year old Mac mini Desktop. During the test my wife is also connected using our connection though the router (works from home) using a power line adapter to the router.
Her company supplied Dell Workstation is pretty involved including vpn to her corporate headquarters, internet office phone set up, also our home phone line uses the router as well.
Here is the router I use and its been $100 for years =
https://www.motorola.com/us/mr2600/p
Here is the speediest site =
https://www.speedtest.net/
Here is my result on my 300 Mbps service, wifi connection with router two rooms away.