You've gone a similar route to me, then.
I have an 8800NL (but the original version), with a standalone access point for 5GHz and 2.4GHz on two separate SSIDs. The 8800NL does still pump out 2.4GHz on a "backup" SSID, but it sits largely unused. We're in 2.4GHz hell here, so tend to prefer the 5GHz spectrum if possible ... and our first foray with TP-Link hardware suffered like you.
One big difference is that we have a SamKnows whitebox running tests (don't ask about the volume of data), so it is the only thing plugged into the 8800NL's LAN. I then have a large switch behind this, which everything else is connected to, though there are secondary switched in the TV corner and in the office.
I don't think the 8800NL has crashed ever/much - 80/20 FTTC is stable and stays up forever - but we have had one anomoly ... when streaming BT TV channels (ie multicast stuff), the 8800NL would regularly start to suffer issues with some of the other devices connected - in particular, wireless devices would either fail to get an IP address, or would fail to get DNS responses when first attached. This problem seemed to go away (possibly after an upgrade), but I'm no longer on Plusnet's TV trial so can't debug any more. The problems would, at first, cause me to manually reboot the router.
Otherwise, things seem very stable. Uptime is currently 138 days.