The big issue with the goons wasn't the Hornets. It was the Falcon/Firefly/Hoplite/Shogun that had stopped all production & were very very rare, along with the Imp/Annihilator that were never before seen & to a lesser extent the Marauder-II plans.
The big issue with the Dragoons wasn't any of the mechs they had, it was simply assumed that they had found a large Star League cache in the periphery, which, canonically, had shrunk in size over the centuries. The really big issue that drove all of the house intelligence services to distraction was the fact that a merc unit consisting of five regiments of mechs appeared one day using odd customs and simply offered their services to House Davion.
It had been theorised forever that the Dragoons were ex-SLDF troops who had returned home, but no-one had definitive intelligence.
Personally, I never liked the FASA era Dragoons story arc, they were one of the very few openly plot driven units in game, and drove suspension of disbelief to extremes.