Maybe you're forgetting about opposing expansion attempts? this is where the game is at in powerplay. Let me explain.
Fortify and undermine are all about the economy of your power's CC reserves. Fortifying your systems is attempting to remove the CC cost of those systems for next cycle. what else is CC used for? Expanding: How many systems you can expand in to, and to a lesser degree 'which' systems are more sensible/viable (higher CC reserves enables you to adopt a more risky/aggressive strategy, going for a less economic system that's in a more strategical position, for example.)
Undermine is then, the equivalent to raiding your opponents mineral line in starcraft. It won't win you the game (expansion, map presence and front line action will) but it will certainly hurt your opponent by damaging their economy and so put you in a better position.
This is what Fortify and Undermine function as in powerplay.
The real action happens in what gives your power it's actual presence in the galaxy. It's ability to expand onto now areas of resource. And the ability for opposing powers to oppose those attempts.
Expansion and opposition is basically "the front line". It's where all the real power plays happen. especially when the powers begin trying to expand in to each others territory.
To make this point clearer, FD have made the thresholds for expansion and opposition dynamic. This means that for an expansion to be successful the expansion value has to be higher than the expansion success trigger value and the opposition value. What this means is that you need to constantly top up your points above the growing threshold of your oppositions, for the entire cycle. the highest at the end, wins.
This is the core of the PP game. Fortify and undermine have their place as an ability to tip the economy more in your favour and away from your opponents', but it certainly isn't what we should be focusing on as a central strategy in powerplay.
