It occurs to me that Shaw knows his ship, his team, and himself. You should know your strengths and your weaknesses. Not every captain is Horatio Hornblower or Admiral Nimitz. Not every ship is the Enterprise with a miracle worker engineer. Not every staff is battle hardened.
That doesn't mean he's bad, that just means that perhaps battle isn't his STRENGTH. The Titan isn't bad, but it may have a load out and engineering team more suited for exploration. The crew may be great, but YOUNG, or simply inexperienced.
Shaw is at least adequate enough to judge a situation, or he wouldn't have enough political ability to be a captain. He may well have realized that whatever these two are up to (and it is likely highly unsanctioned and cowboy-esque), his ship IS NOT best suited for it.
In my job I am a great thinker, a deep thinker, and can analyze with the best of them. I can anticipate problems, make things run smoothly, debrief out of situations so it doesn't repeat and have great people who report to me. But I am not the best snap decision maker. I've trained myself to be BETTER at emergency decisions, and I can do them quite well, but I'm never going to be the best and I've gradually become okay with it - by being the type to mitigate the NEED for emergency decisions.
Shaw, the Titan, and its crew may be the same way, and he's accurately judged himself, the ship, and the crew verses whatever these two genuine legends are likely to get themselves into.
That's my compassionate assessment.