Because nobody uses t2 engies on the front to make factories or radar, there is no overlap in purpose here. I can't use my sparky to make a field base because it can't make 2 of the major key points in a field base and instead I need to go and select my t1 engies in between my sparkies to go and do it, it's pointless micro that adds nothing beneficial at all.
All sparkies having less blueprints does is force you to bring t2 engie to build radar or facs with a sparky drop which is just pointless micro and doesn't do anything interesting for gameplay, especially since it isn't like sparky drops are so massively OP they need to have 0 way to get these tools if the t2 engie is sniped by some t1 bombers before flak is built.
Beyond drops, the only other situation is having your base t2 engies which you barely make any of in the first place replaced by sparkies.
- If that's such a big worry then make sparky cost more
- The benefits of encouraging a more aggressive t2 stage that plays differently than other factions outweighs losing 1-2 t2 engies