I agree. With the TEC Rebels, their pacts should be more oriented to combat and the like, while the TEC Loyalists should have pacts that deal with increased trade and attack/hull while in a friendly gravity well.

These two factions both have different approaches gameplay wise (turtle or attack), thus their pacts should reflect their methods of survival/gameplay.

Agreed. I was surprised this is not the case.

In Trinity, when I teamed up with a buddy, we always made sure we played a different race, so we could double the pacts between us, compared to an alliance of the same races. This should be (at least partially) the case for factions of the same race.

Also I think pacts between same races should get a bit strengthend. You only get half the bonus from allying with a same race than with another race I think? (Though maybe that has a distinct reason?)

So, changing Rebel and Loyalist Pacts a bit from each other would also solve that issue for a part. 1/6 you can't ally for full bonus is a lot better than 1/3 .

How about   Trade - Efficiency - Siege - Thruster

and

                  Trade - Efficiency - Armor - Supply? 

No need to come with new pacts, 4 instead of original 5 per subfaction are just fine 

Since the siege pact buffs attacking planets and your planets durability, maybe split it?

Loyalists get entrenchement pact: provides the defensive half of the siege pact bonuses, and reduces cost and construction time for upgrading planet toughness? Maybe provide a direct bonus to planet health.

Rebels get bombardment pact: provides the offensive half of the seige pact bonus and ... i really have no idea what is doable. A bonus vs structures?  Reduction to supply cost of siege frigates? More of that money for bombardment thing?

Loyalists could get a new pact (no idea for the name) giving extra tactical slots. I know the Vasari had this in 1.2 and before so its doable and would be so in theme it's not funny for a faction with turtling as a MO.

Rebels could get at tech 8 the ability to share the allied with neutrals bit, but that doesn't benefit them since they would already have it. It could boost Insurgency, but that wouldn't be a good as long as insurgency still has that issue with acting like neutrals for the peace with neutrals tech

A pact buffing solid weapons wouldn't be at all workable. Advent doesn't have them at all, outside of things a rapture mind-controlled. Ditto for one boosting missiles.