GreenTengu
Adventurer
I would just be careful how often you use this. I think it may lead to players feeling a bit like add-ons to the DM story or quest of others and not their own. Be careful the weasel or angel does not become the powerful DM-NPC.
From what I see presented, this generally shouldn't be an issue. What you are referring to is the common situation where the DM places an NPC that the PCs follow around and is so very competent at handling everything that it is no longer clear why the PCs are part of this story. And if that is an issue, by all means it should be avoided.
I think there are other ways one could screw up the balance too.
If both sides of this encountered conflict are way too weak, the players will just wipe out both sides without hesitation and thus ruin any deeper meaning.
But for low to mid level adventures, I see little issue with there being two forces aligned against each other with neither being particularly labeled "good guys" as to make the choice of whom to side with just well... obvious, likely with absolutely no real opportunity to choose the either.
It has to eventually become stale for the party to just wander around and kill everything they encountered or that you always have Dwarves vs. Goblins and always, always, always side with the Dwarves without needing to know the first thing about the conflict. Such situations lack any actual player agency or choice and are basically hand-holding adventures even if you let the PCs decide which room to open first.
However, if you have a situation where you have to forces in conflict, neither of which the PCs can just utterly wipe out clear on their own, neither of which can really be easily and thoughtlessly labeled "good" and the other "evil", yet both desiring the contributions the PCs can bring to their efforts... that can make for a far more interesting and intriguing adventure. In fact, you could center a whole campaign on the conflict.
When there is no "right" choice and "wrong" choice, just choices that must be made and carry with them consequences... that is when you actually have player agency and a story.
And you can most certainly have the player's contributions be impactful and meaningful without having them followed around by some super powerful NPC who does all the work nor having them single-handedly win the conflict for either side.
No one soldier ever won a war on their own, but that doesn't mean such wars didn't have heroes.