In fairness, the Pyron kind of sucks; its a pure status whore machine thing, but its damage just isn't there and its not worth working with.
The Big Owl...there's one fight where the game encourages you use it. Think its even the fight you first get it; there are those big massive cannons that are annoying to get around, and Big Owl can snipe them and OHKO them, and you have just enough ammo to get them all.
In any event, its easy to forget Big Owl exists cause its one of those limited resources that you are too conservative on, especially when you get the final upgrades and its one shot of absolutely ruthless damage (instead of several shots of nice strong damage that can be fired just about anywhere, and hit a decent radius, IIRC.) Its easy to refill it at shops and such, but within a dungeon, you typically save it for a boss, and when you face a boss, you often forget you have it altogether.
(and then there's the Dark One who is a rare fight where they decide to remove the thing altogether -_-.)
So yeah, Big Owl is a forced thing; upgrading it isn't, granted (though, think the ultimate upgrades were all store bought stuff in the final dungeon anyway, so its not like they're hyper obscure), and it is easy to forget its existence for a number of reasons.
