Edit: quick t16 map to show how it plays https://www.youtube.com/watch?v=3Dyhknoww-I (sorry was trying to show it clean but clicked a couple of sulphite buffs by habit towards the end )

Just sharing my experience with my league starter, Earthshatter champion scaling max valour with Defiance Banner and War Banner: https://pobb.in/P8WpioaLhSFx . Character is obviously very unoptimised but I'm in softcore and have done 4 watchstones, the 3 new bosses, and a couple of t17s so have been making pretty smooth progress.

I'm running around maps with permanent 215% movespeed, 1k regen, and suppress cap just from 1 banner. Combining 5 valor on warcry with multiple autoexerted warcries, increased valor gained, lingering banner effect, slower buff expiry runegraft (doesn't show in pob), and champions valor refund on leaving a banner

means that even if I press 0 other buttons, I can run around and just press defiance banner every 4-5 seconds and the buff will be up permanently. On bosses/strong enemies I can drop war banner too, easily sustaining both.

Thought it was at least strong/interesting enough to share:

Defiance Banner:

~170% movespeed

190% suppression

War Banner

95% more damage

Bonus Banner Effects:

120% all ele res

600 life regen

3x endurance and frenzy charges

Investment required:

2x ascendancies, 13 points on tree, 1 extra button to press every 5 seconds while zooming to maintain buff, one time setup of both banners on a boss (need to replace every 20 ish seconds)

The investment is non-trivial and having to place defiance banner frequently while running is a bit annoying, but the power was very surprising to me. I experimented with switching to VFOS and the new penetration ring to take advantage of all the free res but I didn't really have enough res still to make it worth it, and couldn't be bothered trying to optimise it more with a lower reduced fire res roll, maybe purity of fire, etc.

Hope this is useful to someone.