The talks wouldn't have been a waste. Think of it as the stepping stone towards the final goal of getting rid of the technique once and for all.
Just a positive way to think of that 'might as well void it'.
Well, the point of nerfing it was to take away a large part of its strategic value; it is one thing to have summons in battle (that now I have to start counting, as apparently they do have a bit of a time limit, though it seems long) but another to have another shinobi on the battlefield. Hardly anyone wanted to have to deal with two shinobi vs one (except maybe people like Kirk and Zenaku, who would take it as a challenge).
With the chakra pools that people, the users in particular, have, 20% of permanent chakra while using the technique is hardly 'tired' status, especially if they use it at the beginning of the fight. Oro didn't personally fight Hiruzen that much during the fight after the summoned those zombies, but oh yeah, Kabuto went full fight while his were active (mastery a SL teacher would have I suppose).
Besides, if the summoner cannot perform an offensive action, then the zombie in question seems to be the main attack/Defense force. It was figured that that was fair.
But... Well, if the summoner can attack if the zombies are not under full control, then in theory, that would give the zombie a chance to break free, if they so choose. So that's one way to look at I guess. But that would be a moot advantage if the summoner's friends were said zombies, or people who don't RP their zombie character.