Thal wants the player to engage more with Combined arms.
That is instead of spamming lots of one unit and conquering that way, we build various units that serve a specific role.
Upgrading scouts to Vanguards for the sake of it doesn't answer that question of what is its role.
Archers are weak against horses so we protect them with spearman.
Warriors are useless by themselves against cities so we bring archers.
That sort of thing.
Siege engines are vulnerable by themselves and lose 1 turn in setting up so what about going down the scout upgrade to vanguard path so that the vanguard's greater mobility means we move them into position first and fortify and then move the siege units up and set up.
Hopefully the AI attack the vanguard first and leave the siege unit alone.
Then any RECON promotions the Vanguard has gained, like Survivalism etc. keep it alive to protect the siege unit.
Now the Vanguard has the role of advance recon and protection for siege units.
In the same way Spearman type units counter horseman types.
Just brainstorming here.