I think the problem with Echo ult is that it charges too slow. The HP nerf is fine because having two full hp tanks can be op and I think that defeats the purpose of her ult. It’s meant to be a way to use someone else’s ult and simply existing as a full HP tank would make it so getting ult isn’t as necessary. However getting the ult takes too long mostly because of the changes to how ult charge works in OW2 compared to OW1.
The way Echo ult works is she gains ult charge 6.5x faster. The first big change is that damage to tanks gives 30% less ultimate charge. Also before OW2 was released Echo got a 15% ult charge nerf. This was done back before she had a cap on tank hp and this was done because having three tanks felt op. Also the way armor changed in OW2 means she gains less ult charge. The 30% dmg reduction for armor means burst dmg abilities are less effective vs armor. So Echo sticky bombs which used to be good for farming ult charge off tanks is less effective in this regard.
These tank and armor changes also effect her during her copy. This also means she gains ult slower not only in her base form but during copy as well which sucks because you have a tight window to gain ult during copy and in OW2 that window is even smaller not only due to the various ult charge changes mentioned but also things like lower hp for copying tanks.
I think the best way to buff her ult is to either increase the rate she charges ult during copy or just increase her overall ult charge. During copy it can be increased from 6.5x to 7.5x. That would be a 15% increase which maybe should make up for the tank changes. Either that or they can simply revert the 15% ult charge nerf she got in OW1 since it was made back when she got the full hp from tanks.