Home Network Help

Hello fellow Redditors, My dad purchased a NAS (a Qnap TS-453a with 2 WD Red Drives) without telling me and greeted me with the box when I turned up for my break. I'm in law school so home networking is hardly my forte. However, installing 5 wyze cams has brought me more street cred than I deserve and I would like to hang onto my new found notoreity. In pursuance of that goal, I read the manual and did some extensive Reddit reading before setting it up. The current set up looks like this:

Main Router (Dlink DIR-825ACG1, supplied by the ISP) --> Access Point (TP-Link Archer C7 configured as an AP; connected through a 15 meter long CAT 6 cable with 10/100/1000 ports on both ends) --> NAS (Qnap TS-453a through two CAT 6 cables with 10/100/1000 on all ends)

I've carried out a few data transfer tests over the 5ghz networks broadcast by both the Main Router (the Dlink) and the AP (the TP-Link) and the speed seems to be capped at 10 MBPS. I've used my laptop (which has a 2x2 WiFi card) and my phone over both these networks and have never exceeded or dipped significantly below the 10 MBPS mark which makes me think that I'm running up against some sort of bottleneck. For context, I've observed significantly faster speeds over the same networks while using it for direct downloads and streaming etc.

Anyhow, I've the following questions and, needless to say, would greatly appreciate any help from you good people:

1. Is the Dlink DIR-ACG1 the bottleneck here? Should I switch the TP-Link Archer C7 with the Dlink? Will replacing it with another router help?

2. Are transfer speeds over 5ghz capped at 10MBPS? The speed plateaus around that point regardless of where I am (the main tests were carried out within 5 feet of the respective routers).

3. Is local routing disabled in AP mode? Is all the data routed through the Dlink even when I use the TP-Link's 5 ghz network even though it's being sent to the NAS directly attached to it? That could explain the near identical speeds over both networks.

4. Is there anyway to set up this network in a more efficient way?

Thank you so much for your time and thank you in advance for any advice you may have!