A response from someone, who is happy in research of biosciences:

The personality of your boss is very important. I always payed a lot of attention to my emotional responses to potential bosses during interviews. Privately asking for the opinions of their subordinates can also help. As you write below, your boss "is widely regarded as a bit of a tyrant". There must be a way to find out in advance next time. For me, the meaningful topic is not enough to save the job, if the boss is a toxic person. On the other hand, the less sexy topic can become meaningful, if the boss lets you follow your curiosity and your ideas (within the constraints of the budget). The working hours are also boss-dependent.

However, I must make one point - I am not saving the world or hitting for the Nobel price. My goal is to play and be somewhat useful to society while doing that. None of my papers is a dramatic thing, it rather feels like a tiny drop into the ocean of knowledge. Some people at lesswrong say: if you do not perceive your topic as the most important issue of the world, change the topic. This is the test I would not pass. I just hope to be a little helpful.