But they're still there. Unless bunker-busting capability completely negates fortification to the point of obsolescence, this capability isn't "0" or "1".
To be frank - it doesn't negate them even them, they simply go down from the status of fortification to the status of highly favorable terrain(even medieval castles still can function as such).
Furthermore, even with ideal PGMs, mapping things for destruction isn't a game of one.
There are fake/new positions, more durable bunkers, old positions may be optionally manned, making it into a guessing game.
No one can guarantee they'll be destroyed before they'll get their job done(poor Seul). Or that paying attention to empty bunkers won't let a gun hidden on the hill next to the bunker do the same job.
Which is the exact problem we have here.
Fortification typically isn't meant to be an "impregnable bastion of freedom against communist devils". Fortification in a broad sense buys time. For this - imho - Penghu is still viable.
I.e., paraphrasing, a certain technical solution(drone observation) will solve essentially a geographical problem.
Maybe it will(it indeed often happened in human history), but it needs to be seen. More often than not, however, when we're talking about sides at the approximately same technical level(of understanding warfare), the opponent won't play it dumb, and there is going to be a need for organizational/tactical solutions.
If anything - I personally think if anything will put the resistance down rapidly - it will be breaking morale (which indeed can be destroyed by firepower).
So was Iwo Jima, and the attacker didn't really have to care for collateral damage.
How proximity to a large body of well-protected friendly territory can be a detriment?
At best it can be useless, if complete isolation&supression of both is to be achieved.
But anyway, Penghu location(much like Taiwan itself) is a big problem for the Chinese side - it really decreases available firepower options.
