That's true, though non-adjacent Powers would be getting the Beyond Frontline Penalty in addition to any System Strength Penalty, which would make them very inefficient.
The problem is that if the game is balanced so that a theoretical 6:1 ratio (allowing for BFP but without SSP) or even 12:1 ratio (assuming the defenders focus their reinforcement around High/Very High SSP systems) is an even-ish fight for undermining versus reinforcement, since that never actually happens in practice all it means is that everything gets hyper-reinforced.
Every week so far has seen a massive surplus of successful reinforcement over successful undermining. Powers losing systems of any sort, but especially Fortified/Stronghold, is generally rare.
Of course, players aren't split nice and evenly between the 12 powers in the first place. If Aisling Duval were to decide to attack Zemina Torval, well, that's just one power versus one power but Inara estimates a 13:1 numeric advantage for Duval. If everyone else gangs up on Torval, that's a roughly 60:1 numeric advantage. Do we need undermining to be 60 times more difficult than reinforcement just in case the YADAJAFNELP coalition goes for her?
At some point an outnumbered side just has to lose.
I haven't specifically tested Reactivation, but they certainly work for Acquisition, and normal donation Support missions work for Undermining, so I'd be surprised if they didn't.
I guess today's task will be to find one and see what happens.
So the friendly-system Power contact taking all the goods and data you also stole doesn't take the regulator? Definitely sounds like a bug, that.
EDIT: are you sure that Power Regulators are allowed? I can see "Energy Regulator" on the hand-in list, but not "Power Regulator".
(It's entirely possible that in a non-English translation they've ended up both being called the same thing, of course...)
What I have noticed is that the top 10 of most of the powers is very similar, with a few players around 1 million and the lower half of the top 10 around 500 thousand. This seems to be independent of Power "size" (except for patreus). It doesn't matter what % of the player base you have, it only matters how much those players play, Like in powerplay 1 there is a small cohort of players who will do the brunt of the strategic work and the rest just get to stumble around and do their thing.