They also could have increased their stockpiles of old SLDF fighters through negotiations with fleeing Blakists. They could have even found a large SLDF cache.
The Hanseatic league already has quite good designs, which they produce by themself:
1. The light Centurion-fighter is superior - compared with IS-designs like the Thrush, the Seydlitz, the Cheetah or the Sabre. It is also better than SLDF fighters like the Trident, and the Swift.
2. And the heavy Vulcan ASF has a really good punch with its 2x AC10, the Large + Medium Laser and the SRM6.
I also asume that the pilots are well trained in the Convoi Protection Force.
But what means "well trained" in relation to a periphery-state?
I consider an avarage pilot of the hanseatic League as inferior - compared to an IS-pilot who (for example) completed the Sun Zhang MechWarrior Academy.
And the Clan-Pilots are geneticly enhanced.
Also the Clans have superior hardware. Just take the Batu ConfB with all its Pulse Lasers.
To counter these advantages of the Clans (better pilots and better hardware) the Hanseatic League would need a numerical superiority to keep the balance. And the manufacturer on Antwerp is producing the hardware in low numbers.
So they have to adjust their tactics and to try fight in asymetric warfare. Attacking supply routes and so on.
Or - as mentioned before - they have to use nuclear weapons (which would be the tactic of a fanatic state which would not hesitate to use the scorched-earth-tactic. I personally doubt that the mercantile Hanseatic League would use such a tactic)
We should also keep in mind that the planets of the Hanseatic League are not so populated and dont have the same infrastructure like those of the IS-major powers.
The HL does not even have Hyperpuls-Generator-Technology.
I cant await Aug 7th, when the Operation turning Points "Hanseatic crusade" will be published.