I know the AC1200 units only support a single unit when in bridge mode. I think this is a huge limitation for the following reason: Let's say you have both wired and wifi devices in your network. You want them on the same broadcast network (same subnet) because the application protocols require it (e.g. a phone app to detect and control your a/v receivers.) This isn't possible unless you make the primary AC1200 the DHCP server/main router for the entire network, which isn't optimal. (I have a "real" firewall that fronts my entire network and handles DHCP). Or you only use one AC1200, which defeats the main benefit (multiple wifi access points). Or you put everything on wifi, which may not be possible because some devices have hard ethernet ports only. I like the AC1200 but this seems to be a show stopper in this situation, and I don't think it's that uncommon.
I definitely understand what you're saying about the limited functionality in bridge mode. While there's no way to increase that functionality in settings, it is something I can pass along as a suggestion to our internal teams to look at and review. Thanks for sharing your input. If you need anything else, please let me know.