Even if the upgrade were mandatory, players would still delay purchasing it until after the T70.
Often these days tier 3 is only built once the necessary resources to also purchase the T70 are almost available. By removing the HQ upgrade requirement, you potentially reduce the timing when a player would feasibly buy conscript upgrades by up to 3 minutes-as players will be incentivized to build tier 3 much faster.
What are you talking about? You can already choose to ignore the upgrades until after t70 now
But if you built 3-4 cons and don't have mollys OR AT nades before t70, you are in for a rough time