As the saying goes, Like Farher, Like Daughter

It certainly runs in the family!

Wasn't Fenrir generally trying to help Sunny get a better control on her growthsplosions? Feels kinda weird to see that he's now struggling to even control his.

He has a far easier time of it around mortals rather than divines, but even then, this is still quite a bit more controlled than Sunny!

Is it really? Growthspolding out of a building is still just like Sunny. Yes, he might not be as big, but that's not really relevant, as that doesn't actually make it seem more controlled.

It is, both in terms of final size, and in Fenris having a potentially-avoidable trigger condition while Sunny does not.

I really don't think it is. The final size as shown is something we see from Sunny regularly. And the trigger can be "a stammered compliment or a flattering thought". That doesn't sound particularly avoidable.

... Good for you? I think? Where are you going with this, are you trying to police me (incorrectly) about my characters' own lore in the comments of an artist's upload?

I am disagreeing with your explanations and stating why I feel the way I do. If you feel that is incorrect, that is your right as they are your characters. I made a comment, we talked. There is no policing.

It is generally unwelcome to go around telling people "I disagree with the way your lore works based on what I've learned about them and think you're wrong," if you don't understand the lore and want to hear more about it to understand, then you can just ask. You do not need to interact like Pursuit is playing in the background.

The size we see here is likely not the final size for Fenris, and is rarely a final size (often it is a starting size) for Okamitsune, and either way they are drawn art posed and scaled for visibility and effect, which is a thing I usually try to encourage artists to do when drawing my characters given my characters often posses extreme innate variability in shape/size/appearance/etc. and I generally don't mind something being slightly off-canon or pseudo-canon if it helps make a better picture.
Divine beings in my lore encompass a wide range of entities, some of whom may have a significantly easier or harder time managing emotions/reactions than humans we are used to, such that for many of them "avoid strong appreciative reactions" is not an implausible request; even if that were not the case, "is not always able to self-regulate his size (without mentioning how rare or common such a loss of control is compared to maintaining control) at the occurrence of specific triggers" is a far cry from "is going to randomly growsplode sooner or later in literally all scenarios, almost always sooner and often continuously after." And context is also relevant for the comparison, insofar as being in a highly divine-energetic environ like a pantheon makes all three Æsir more likely to growsplode than their base scales, such that Fenris and Inari can manage stable sizes almost indefinitely among properly isolated mortal avatars in fully mortal environments, while Sunny is catastrophically growsplosive in all forms and locations.
This is all setting aside creative liberty and different interpretations of characters, and also ignoring the fact that this could 100% simply be a picture of Fenris in his earlier days as head of the Æsir pantheon, countless multiverse-lifetimes before Okamitsune was even born, in which case he'd be learning the very self-control he now makes a consistent effort to impart to his daughter. And also probably other things I'm not remembering at the moment too.

I have been in the furry community designing and evolving characters for over a decade and a half, much of which is not available to review online. There's a ton of lore for these nonsense goofs who outsize universes/the concept of size itself, it can be nice to ramble about it and share. But I normally try to avoid loredumping multiple paragraphs of hyper-situational explanations and logic out of nowhere when a sentence or two of summary should do the job.

Edit: remembered another factor, Fenris' size is also more stable within Æsir cosmi due to their design; visiting external pantheons requires more preparation and focus to stay size-stable.

To be honest, there's a lot I can say about this, but in the end, I'll say this only: having much of the general and finer details of the lore be something only in your head seems like a waste of characters and writing. It would be better for everyone if you just posted this stuff on your own FA page like you used to.

There's really no reason not to, I feel.

I can think of several reasons I don't? But I also don't need "reasons" to chose not to, and claiming it'd be better for "everyone" if I did is downright disturbingly presumptuous/insulting, so uh.
Would you maybe accept "my employment and general life situation are not what they were a decade and change ago?" Because that's more than needs sharing but I get the impression you're going to make this weirder if I don't give you some kind of justification.

"a waste of characters and writing" good lord

He gets surprisingly few complaints about it, at least! Lovely work, thank you again for drawing the big buff woof <3

I wonder who handles their compliments and complaints department. I assume that would be a Charity thing if not Inari.

You're welcome though!

That tends to be delegated pretty far down to the nearest local representative, but everything headed up for the Æsir does get routed through Charity first, usually!

So, realizations of "Oh no he's hot" causes this to happen? Hard to imagine that stopping before it makes him go infinite!

Stray "Oh no he's hot" thoughts are probably the number one cause of Fenris growsplosions. It seems to happen quite a lot!