Not necessarily. I think they were right not to start trying to recruit people after David. For one thing, there was just now way of knowing who was and who wasn't a controller. Secondly, Visser Three maintained the passive invasion under the assumption that there was only a handful of Andalite bandits running loose and one possible human with the morphing technology.
The Animorphs had to recruit the auxilliaries because their cover was blown and the Yeerks knew who they were. But as long as there were only six of them in the earlier books, the Yeerks wouldn't raise the invasion level. Increase the number of Andalite bandits, thus increasing the amount of damage to the Yeerks and the Empire might go ahead and greenlight a more aggressive invasion.
Now I agree that the situation with David could have been handled more appropriately. At the very least I don't think they should have given him the morphing power at all, but since they had done it they could have treated him a little more amiably. Poparena makes alot of good points and when it comes right down to it, the David trilogy was one mistake after another on behalf of Jake and the team as a whole. Everyone had their hand on the idiot ball.
Now...offering the Yeerk Peace movement the morphing technology might have been a smarter move. We don't know how many of them there were but it's safe to say that Aftran had a significant amount of people on her side.
Give those a Yeerks a chance to take permanent morphs in exchange for surrendering their hosts and smuggling out weapons and other equipment that might give the Anis an advantage against the Yeerks. Heck, if the Anis had acquired Yeerks, they could use the freed hosts to infiltrate the pool and smuggle out even more hosts. Stage the deaths of said hosts and make the Chee earn their effing keep for once by having them house the freed human hosts while the Hork-Bajir return to the Valley with Toby.
The Yeerks would panic at a larger fighting force of "andalites". But a few hosts going missing might barely register on their radar. Visser Three clearly didn't care about a thousand Yeerks dying or becoming addicted to oatmeal, so this would be another great way to use his tunnel vision against him.
Give Toby the morphing power. It would be easier to coordinate the escape of more Hork-Bajir.
Sheer attrition alone wouldn't be enough to slow down the invasion, but the fewer hosts the harder it would be for the Yeerks to maintain security and secrecy.