I was using my Samsung SmartThings v2 in bridge mode while using my Ac66u w/Merlin for management. I gave up on that setup with the Deco.
The Deco can be placed in bridge mode as well and the AC86u can be your “gateway” for DHCP, scripts, Custom DNS, etc. just turn the Wifi radios off. You will lose some the Deco features and you may not care for them anyways. I forget what you lose.