That… is… what tiers do, though. They force a linearity to unlocks.
I agree that this is very awkward, now that the Cybernetics Core’s only other research is Warp Gate due to Hallucination becoming default and the removal of ie. Singularity Charge.
However, the simple thing is that the SC2 tech tree takes a huge amount of its construction from the SC1 one, and that if Protoss did not have some structure between Gateway and Stargate things would be very bad.
You could entirely remove the Cybernetics Core by making the Stargate require the Twilight Council or Robotics Facility; for example.
But like… “answer to problem” – what problem are you imagining that putting air upgrades on the cybernetics core is avoiding solving? I agree it’s really odd that Protoss is the only one for whom neither upgrade structure cost gas. But that’s not a ‘problem’; and neither is the location of the upgrades?
I genuinely don’t understand what you actually meant here.
Do you mean making it work like Ages in AoE where you need two of Archery Range, Stables, Blacksmith, or Market to tech up? That’s the only way I can understand ‘nonlinear extra steps’.
Which just also doesn’t make any sense seeing as you complain about how AoE’s tiers work three lines up.