I'm pretty certain Optimus was talking about Ratchet there, not Bumblebee--he was looking right at him with a slight smile on his face. Ratchet's attitude may have stemmed from his inability to heal Bumblebee all those years ago. Ratchet went from a field medic to doctor; I know there might have been a few hundred or million years there, but for a Cybertronian, it may not have been that long. Ratchet, being one of a few Autobots left may have had to really pick up the reigns and make due, and for someone's who's first job or at least first important one, repairing a scout with vital news about Megatron may have been too much--failing most likely made matters worse. Ratchet's inability to make human computers work with Cybertronian tech; his inability to build anything better than a ground bridge as well as his inability to successfully reconstruct synthetic Energon may all have to do with what he couldn't do for Bumblebee back at Tyger Pax. I wonder if we'll see Ratchet working on synthetic Energon any time soon and perfecting.