@techie_19 

I have the exact same router as you and a very similar range and number of devices connected.  I have absolutely no problem getting and keeping the devices connected to wi-fi.  The difference is I am not on the latest firmware I am running the previous one (1.2.2 ) and I have disabled QoS.  

You can try the following and see if it helps:

1. Go to "Advanced" and the "QoS". Choose "Standard" for Application Priority and make sure that no devices are set to use QoS in "Device Priority".

2. In the firmware that you are using there is a setting (I think it is also in the QoS settings page) that allows you to set the download speed you get from your ISP.  Make sure it is set to 200 Mbps.

3. Reboot the modem and see if the problem is fixed.

If the above doesn't fix your wi-fi problem you can always download the 1.2.2 firmware from the TP-Link website and "downgrade" your firmware and apply the above changes.

Good luck!!

@techie_19 

When Xfinity upgraded my service to 200, I found that I had to power cycle the modem and router like you would to get a LAN IP address to get the faster speed. I have a slower older Archer C8 and running 30 plus devices. I get around 230 wired and close to that on 5 GHz when close to the router. As a test, you may want to bypass the router and connect a PC direct to your modem with an Ethernet cable and see what speed you get from your ISP. If you are not getting over 100, you may need to replace your Ethernet cables.

My router does not have Smart Connect and I would not use it even if it had it as I prefer to control which bands my devices use and because what others have reported about it. IMHO Smart Connect can do a fair job, but is not ideal for everyone's network. For example, it may put your PC and TVs on the slower band because it gets a better signal and the smart bulbs on the faster band because it gets a better signal. Others reported that moving from one band to the other when moving through the home can be problematic.  

I would also open up the number of assignable IP addresses. If you have a VPN, that can cause an issue. Using cloud based backups can over tax the network such as those provided by Google and Amazon. Depending on how some security cameras are set up, that can put a heavy load on the network also.