@MulletMarmot,

A few things:

Is your fiber modem in IP Passthrough or Bridge Mode so that you are not creating  a Dual-NAT situation with the A7?

What is the speed seen when connected into one of the ethernet ports of the A7? Wired and wireless speeds are difficult to compare, so a wired connection to the a7 will allow us to determine if the Archer is receiving the full bandwidth from your ISP and if performance is affected for all traffic passing through the Archer router.

What wireless speeds were you able to achieve prior to the decrease?

I would verify that both the 2.4GHz and 5GHz bands are available - the speeds you mention could potentially indicate that your devices are connecting over 2.4Ghz, which has slower speeds. Check the LEDs of the Archer or the management interface for this.