Think of it as 'useful'
Its a very potent card and the reality is that in a high level rpve game, this card is a staple.
It's very risky to use in 2v2 (using this in 1v1 is not viable on an even skill level)
Binding 150 power and ensuring it survives for the duration of the build time (no idea how long that is) and then 60 seconds for the ability cooldown and then killing enough units to make it worth using can be extremely hard to pull off at the power disadvantage you put yourself in. If you can easily do this then you have already won the match and there are better options to end the game quickly.
When asking if a card is OP the first argument (like it or not) is always whether it is majorly affecting the pvp balance. If not, does the card have a game breaking effect on pve?
If it is blatantly overpowered (LSS anyone?) then yes it may end up on a watchlist.
At the end of the day, if the pvp balance is not affected, there would need to be a large outcry from the community to get the card considered for balancing.
Was SoW on the watchlist at one point? Seem to have a vague memory of it for some reason. if anyone knows it would be @Treim