Tier cannot be TF'd, just FYI. Best you can do is 543.
Also, the issue with the 2+2 setup is that 1) to get the max out of t15, you need to use a 3 HoPo WOG (for 15sec of block), and 2) to get the max out of t16, you need to use a 1 HoPo WOG (to get the most efficient use/least wasted HoPo per Bastion stack). So....they kinda work against each other from a "gaming" standpoint
But, they have incredible synergy as a mini-cooldown, provided you use it as such, and not a micro-management "buff" to try and game at 100% uptime.
Also also, like you said, Phys dmg (thus far) has been more or less a nonissue (in 10s).