I have no formal training in biology (much less, exobiology), but I do have a strong general science background and a wide and deep amateur interest in biology, and I agree with the Dragonfly strategy.

We simply don't have enough knowledge of Titan's bugs to be able to design an instrument with a good chance of identifying them. Sure. "spiders" or other macro biota could be easily spotted with a simple camera, but chances are any life on that world will be microscopic and totally unlike in appearance and function to terrestrial microbes, easily confused with a host of weird and unpredictable geological features peculiar to Titan's geology and chemistry.

Any generalized detection device capable of having even a fighting chance of unambiguously identifying the natives would probably be so massive we'd be better off replacing it with other instruments. Just think, if the Titanians launched a camera probe to Earth looking for Life, and it landed in the ocean, or the Sahara, or the Himalayas, or Antarctica, what are the odds it would "see" any Life. I'm sure many valid and worthwhile sensors and detectors have already been ruled out for these reasons because there are better alternatives.

I may be dead wrong (Carl Sagan once quipped the Mariner probe would not have been able to detect Life if it had landed in the JPL parking lot), but payload mass is dear and precious; we have to play the odds as best we know how. Even the old Landsat carried imaging sensors that worked fine, but taught us nothing. The point is, there is fierce competition from many highly qualified investigators to get their experiments flown on any space mission. Unfortunately, they can't all go.