By your measure; defences, CC, barracks, army camps, all lab upgrades, spell factories and pretty much any and every upgrade related to attacking and defending should be instant upgrades too.
Well why stop at that, your resources buildings gain HP with each upgrade which could be construed as defence so lets add those into the mix.
And while we are at it, the whole armies and spells taking time to cook... that is surely a barrier against attacking more often lets get rid of that too.

