People's experiences may differ, of course. I caught Kuno fairly quickly (on my third serious attempt at trying to catch him). Gloom weather is extremely common in Mor Dhona - there's a high probability that Gloom will line up with Canavan's time-of-day requirements many, many times over the course of a real-life day. The Clear/Fair -> Blizzard requirement on Mahar? It's far from uncommon for this to crop up only once in a real-life day, and often not at all.

As for mooch bait, Silverfish seem to bite the bait WAY more often than the two other fish that will go for it (Lamp Marimo and Giant Bass). Cloud Cutters, on the other hand, don't seem to bite much more often than any of the other three Skyfish you can catch. Additionally, Mahar may well be the only mooch fish with a significant chance to slip the line.

I've made numerous attempts to catch Shion, now. I generally see less than five HQ Cloud Cutters during a Blizzard period, and of those I'll maybe hook one or two Mahar, either or both of which may fight free of the line, and either or both of which will likely be NQ even if I do reel it in. Exactly once have I successfully caught an HQ Mahar and mooched with it - the resulting Shionosaurus fought free. /sigh

Still, even that was a bit uplifting, and gave me hope that I will someday finish my fish log! (Shion's the last fish I need.)