The problem with Yar's proposal is indeed "Then what?".
Stopping the plague ship with a tractor beam leaves her intact to depart and travel to other destinations, such as an assigned safe quarantine area. Stopping the plague ship with a phaser leaves her stranded on orbit around Haven! Talk about ongoing effort...
Really, the idea that Yar, or Worf, or Data, would be unaware of the potential of the tractor beam is... Insulting. And if Picard reminded them of the beam's existence, he'd appear condescending. There's absolutely no need for Picard to "bring the crew up to speed" on any "plans" of his, unless one wants to emphasize the unprofessionalism of said crew.
Of course, Picard could just say "Tractor beam stand by" to the benefit of the audience. But he doesn't need
As for only acting in the nick of time, well, it's not as if there was harm done. Picard just gave the Tarellians the chance to turn back or otherwise respond to his ultimatums without escalating the situation. Haven knows these people would be desperate enough without extra harassing!