Used right, they can be very effective.
Too true, I said that earlier. However, like you mention a little later, some are hard to "use right".
The Minotaur is an ambush predator, the Delphyne and Roc are hit and fade units,...
I love the Roc, and my next PM expansion will expand their Point. Interestingly enough the Basilisk 3 pretty much does the same job without running as fast.
I haven't used the Delphyne, or Minotaur, yet, but I do have a love for the Gorgons.
... Satyr is a line combatant,
I think you have the names mixed up. I usually use them like a Cicada. But that's mostly because I'm using the 4 with the TAG, coordinating with the Gorgons.
Erinyes is something we point and laugh at...
Both the Erinyes and Harpy demonstrate that there is no way to have a good 2 ton Protomech. Not enough room for Engine, firepower, or Armor. At 3 tons, we find the Cecerops and Siren which move like a bat out of hell, so they can at least scout. The Erinyes and Harpy can't even do that.
Svartalfar is something we really want the official sheets for the Svartalfar 2...
And maybe cheaper models...