They're probably celebrating that Donaire is now facing Santiago. Santiago is probably not as dangerous as Moloney. Santiago's power is also much lesser than Moloney's. Santiago is shorter as well and has shorter reach also. This match will definitely be a lot easier for Donaire.
And yes it is a title fight. Donaire couldn't ask for more. Of course he is still a strong and dangerous boxer but we all have to accept the fact that as you age you will have to lose a lot of your boxing capabilities. Donaire will probably be more confident this time and will win over Santiago.
If Donaire doesn't want a tougher opponent, then he should be happy with his. The odds aren't yet available, but I believe Donaire will be the favorite. It's just sad that he's coming off a big loss against Inoue, so I hope he's still very confident, and we'll see his signature KO punch again.
He definitely wants a strong opponent but not the toughest. He needs to consider his circumstances. I'm sure his team is also more careful now in choosing who Donaire fights.
I have not yet seen any odds also but it is indeed possible Donaire will come out the favorite, but only slightly not a big favorite.
His loss to Inoue shouldn't bother him anymore. He should've just accepted that Inoue is fighting at his peak while he is already on his way down. And losing to an incredible champion is still worth it.