@Eiranium 

Of course, turning off the whole TalkTalk modem would break the Internet connection.

To switch off just the Wi-Fi signals there should be a simple toggle switch located within a "Wi-Fi settings" menu in the user interface of the TalkTalk hub, like shown below.

Hi, I've turned it off. And the AX1500 seems to still be giving off connection, however it's still behaving the same with intermittent drops in connection. I still don't understand why it would be performing worse than the modem lol.
Actually turning it back on was near impossible because the connection wouldn't stay consistent.

Edit: I tried a test between having Smart Connection on and turning it off and having 5G on instead. And there's actually a fairly big difference between the consistency in connections I'm getting.
Below is with Smart Connect on

And here is with it turned off and 5Ghz on

  @Eiranium 

  @Eiranium 

Was your Archer AX1500 brand-new when you got it or is it a pre-owned one?

Anyway, a good test to find out if the AX1500 has some sort of defect would be to reset it to factory default settings (either via the corresponding option inside the router's configuration interface or by pressing and holding the physical reset button for about 8 seconds) and after it has booted up again test the Wi-Fi connection right away, without changing any settings on the router. The default names of the Wi-Fi (SSID) and the default passwords are printed on the label on the underside of the router. The AX1500 should still be able to connect to the Internet through the TalkTalk hub, because "Dynamic IP" is the default setting of the AX1500.

By the way, have you tested the Wi-Fi connection of the AX1500 with more than one client device? If yes, are they all showing the same symptoms?

  @Eiranium Try removing the top cover of the router; there's two screws on the bottom if I recall correctly.

I have a AX1500 and it was dropping wifi intermittently too. I saw some advice about overheating being the cause, and took the top cover off and put a fan on it. Works perfectly now 2.4 and 5 AC and AX with about 20 wireless devices.

Edit: Just saw you fixed it by disabling Smart Connect; it's possible you have an AX1500 that doesn't overheat. I had an AX1500 before this current one that was seemingly fine with the top cover on, but I'm not sure what the HW version was or if that mattered. My current AX1500 with the top off is HW version 1.26, and it had the wifi issues with Smart Connect disabled.