XB6 Drastically Slower Speeds than expected?

I've upgraded to 600 MBPS download/15-20 MBPS upload. That required me to get the newer XB6.  Both wired and wireless, upload speeds are never an issue. I'm not sure if this is expected, but wirelessly, the very most I will get is 320 MBPS download. And this is only with a PC directly next to the router itself. Just 1 room away, it gets about 150-250 MBPS. I've tested with my phone just about every 2 or 3 feet (Its internet adapter has 400 mbps download max possible, I believe.) and fastest it ever has gotten is just about 250 as well. 

Of course, ethernet/direct connection, the speeds are nothing short of amazing. It shoots well over 600 MBPS. It's just a shame my wireless speeds are shooting so low. Yet, I see threads that are pretty old and people are getting much faster speeds than I get. This begs the question:

Is my XB6 defective? And if so, I'm iffy about going through the process of continually replacing it until I get a 'good' one. And with that said, does bridge mode work with the XB6 currently? I've seen threads about a half year old stating XB6 bridged mode was disabled and because of that, I'm hesistant to purchase and bridge a superior router to it. 

P.S. I've already contacted support the first day I've received the router. They didn't seem too concerned about the 300 MBPS speeds wirelessly and just immediately patted themselves on the back when the ethernet speeds reported over 600 MBPS. Hence, I'd much rather ask the community. 

P.S.S. + edit: I've also verified far beforehand my wireless adapters can handle speeds over 1000 MBPS as well, in case that was a concern for future readers* And yes, I'm on the 5 ghz wifi signal. Thanks.