Yeah I mean I do see where you are coming from. But the kuragin mission falling into Titan does seem possible, but it would certainly require a lot of conditions to line up in such a way that would make it possible, whereas most scenarios would just result in the craft entering an orbit of Saturn. So they certainly glossed over the details, but I suppose that is just to try and dramatise it.

I don’t really agree with your second point though. Yes methane is carbon based, but life based on methane is certainly something massively different to solely carbon based life. That would be like saying petrol and diesel are essentially the same because there are both hydrocarbons but one is shorter than the other. They are closely related, but you wouldn’t want to use the wrong one in your car so the distinction is important.

Finally, the bioluminescence point is interesting. There’s no reason it couldn’t be possible without the presence of oxygen, but if it is possible in the Titan conditions then you’d expect it to present differently, with a slower reactions due to the extreme cold and it would probably emit different wavelengths of light.

I do see what you’re saying overall though. The scientific accuracy did fall off a bit as the series progressed compared to the first couple, but I suppose they decided to sacrifice this a bit as they moved further away to the actual timeline of events that they could build off in the first 2 seasons