True enough. Just remember the whole key here is the Borg's adaptability. I'll bet it's not fullproof either, so it would be an enormous gamble as to whether such weapons would put the Borg out of action first or if the Borg could hold out long enough to either detect and disable the platforms' power source or to assimilate the platforms. If the platforms were really good, it would still be touch-and-go with the Borg.
About the borg:
"The borg shields seem able to stop efficiently only a limited range of armaments at a time - but, once they adapted to these armaments, they're practically invulnerable.
Everyone else's shields protect against pretty much everything simultaneously, but against nothing exceptionally well.
Different weapons philosophies - and technologies.
In the case of photon torpedos, the borg adapt, obviously, to gamma radiation.
Perhaps they don't even deflect or absorb it (like everyone else is doing, according to trek lore). Maybe they send the explosion into subspace (borg shields were referred to as 'subspace fields'); maybe they transform this radiation into neutrinos or another harmless particle; etc.
Whatever they're doing, it protects the cube much better than starfleet&co's shields, and it works progressively better as the modulation (ex - exact frequency/ies) of the offensive weapon is more precisely known."
An effective tactic against the borg is to hit them as hard as you can with your first hit - because, during your second or third hit, your weapon becomess useless.
This is why Starfleet proved its tactical incompetence by ignoring this tactic - for example, they always wasted their new phaser modulation with a few phaser shots instead of, from the start, channeling a deflector discharge hundreds of times more powerful, destroying a large part of the borg ship.
In this context, orbital weapon platforms can be more efficient against borg than starships - primarily because their phasers/weapons are more powerful than those mounted on ships (the main advantage of these fortifications seems to be that they have an arbitrarily large power source and don't have to make compromises pertaining to warp drive&co).