>This gets back to P2: a worldview that entails infinite positive utility is preferable to a worldview that entails losing out on that

The distinction is still muddled. Worldviews are beliefs, and mere beliefs can't have an infinite impact on utility. Actual states of the world can. Pick one of these two:

P2a: An actual state of the world that entails having infinite utility is preferable to an actual state of the world that entails not having it.

P2b: A worldview that commits us to the belief that we will have infinite utility is preferable to a worldview that commits us to the belief that we will not have it.

P2a works with the first set of premises I proposed, since all are about actual states of the world, and P2b works with the second, since all are about beliefs.

The issue with the first set still stands; P2a taken with P3 and P4 don't support P5 since one's beliefs have no relation to whether or not they get infinite utility.

You want to insist that one's beliefs do impact the finite utility they get on Earth. Therefore you should adopt the second version of the argument and stop combining it with the first. You're running together two different lines of thought, and this makes the logic of your argument unsound.

>I would be very interested to hear your thoughts in terms of this analogy

In the case of the boat, the best outcome (survival) requires both that there really exists a means of escape and that a person is motivated to search for that means. In the case of the naturalism debate, the best outcome (infinite utility) only depends on the state of the world, and not on what we are motivated to do or believe.

For the situation to really be analogous, assume that whether or not the passengers can be saved is independent of whether they're motivated to search for an escape. In that case, the similarity you might draw between the boat and naturalism is that in both cases, believing that one will enjoy the best outcome gives finitely higher utility than not believing.

Then the naturalist would give the same response to the boat case as to the case of naturalism. They could possibly deny any of your premises.

>to me it seems like a sort of coping mechanism

To call it this would presuppose that there actually existed an issue that was scary or depressing enough to be coped about, and this is exactly the presupposition that naturalists challenge.

In any case, the important thing to focus on is not why naturalists are giving the arguments they do, but whether these arguments are logically sound. Most acclaimed arguments for objective morality and for meaning in life make no appeal to any non-natural entities. You can make a post on r/askphilosophy if you want some pointers to them. I frequent that sub and see that you've already started a discussion there, so check out the sources that were given to you.

>the very thing naturalists often accuse theists of

What I've seen theists being accused of is having a set of views that are false; whether they are using those views to "cope" is besides the point. According to some naturalists, theists perceive a problem that isn't actually there (ex. that lack of meaning in life, or having only subjective meaning, is somehow terrible), propose a solution that actually isn't necessary (or isn't sufficient) for solving said issue even if the issue existed (ex. seeking objective meaning from god), and bundle with it a bunch of adjacent positions that are implausible (ex. divine command theory).

Finally, I'll say that on the question of whether a naturalist world makes life empty, most people defer heavily to their intuitions. But intuitions aren't infallible, and they aren't all the tools we have for reasoning.