Shiny Horsea > shiny Gible in every way imaginable, even if you think Shiny Horsea isn't particularly pretty. Furthermore, one must consider shiny Kingdra vs. shiny Garchomp. Really, there isn no competition, lol. Bad example.
And I know Garchomp has a shiny form. The difference is so barely noticeable that I joke around by saying it doesn't have a shiny form.
I agree with you on Shellos. But honestly, there isn't a shiny line as bad as the Garchomp line.
Uhh, shiny Gible has a similar colour to shiny Horsea, don't it? Shiny Garchomps are different; the splotches are more bold, IIRC. I will give you Shellos, though...it's poor.
Why breed for a shiny Gible? It doesn't have a "shiny form" just an imperceptible tint (or is it darker? I can't remember). There are lots of "rare" shinies you can go for that don't have sucky shiny forms.