They went from cheap indestructible world destroyers to expensive flimsy annoyances. Some middle ground would be nice; if they stayed expensive and kept their low damage, but got back their high durability, that would be more reasonable.
Actually, its just the opposite. If anything is to be done to the siege frigate, make it cheaper, but DO NOT give them high durability. The main problem with them before was their high durability. It made no sense.
Think about it. Siege frigs should not be able to waltz into any system with defenses, whether those defenses are static D, or a few generic frigs sitting there, and survive to tell the tale. They should instantly be toast if that happens. Their purpose is to take down a planet AFTER ALL DEFENSES HAVE BEEN DESTROYED by the accompanying main fleet.
The way it should have worked all along was - your main fleet moves in and attacks a planet, while siege frigs are hanging back a phase jump away. If your main fleet is successful and toasts the planetary defenses, plus any fleet sitting there, THEN you move the siege frigs in to clean house. This is the intuitive way the game mechanics should have worked all along.
Siege frigate armor should be made of paper. Which means any planetary defenses (even light ones) should kill them easily. Siege frigs should not be able to go anywhere unaccompanied and live to tell the tale. The problem now is not that siege frigs are made of paper (that's good) - its that they are too expensive in terms of fleet cap, so nobody (including me) builds them. If anything is to be done, KEEP THE PAPER ARMOR but lower the cost.
Personally, the original unit was so hated, I never want to see the unit rebuffed in any capacity whatsoever. *BUT*, if the fates deem it necessary to do something, I hope that only the cost is adjusted - nothing else.
By the way, some people have wondered what the problem was all along, since a PJI should have slowed them down. Again, not knowing the crazy history of this game, heh. The PJI was a non-unit when the game first came out. It did nothing. It simply took up a space in your planetary logistics, and cost you money. In other words, it was an expensive ornament and nothing else.