Tyr's stance change has a longer CD than 1s (unlike the others), which forces you to plan your stance changing plan way ahead compared to the others, which is more akin to Fafnir's ult than the other stance changing
The trade off is that Tyr has a CC immune ult, while other stance switching gods (Hel and Ullr) do not.
Tyr's assault stance skills are essentially the same as his defence stance, but stronger - much more like fafnir's ult than any other stance changers
Stronger how? Massive heals and a dash that passes through gods can be seen as stronger tactically, since you can sustain yourself and re-position through enemies. Otherwise, he has a little extra power. Not all that more powerful.
Tyr's stance changing reset the CD on his non ult skills, unlike other stance switching gods, but identical to Faf's ult.
Irrelevant and unrelated to whether it is a stance switch or not. Rat's dash could reset it's own cooldown. Resetting cooldowns is not indicative or special to stance switching.
Fafnir's ult is a kit-wide steroid. All previous stance changes have been permanent (until you choose to change again). While it is very similar to a stance switch, it is not. Nothing is changed. He's not in a different stance, he's just buffing all of his skills. The skills stay the same and then do MORE.
That is a definition of a steroid in Smite, doing MORE. A stance switch is doing DIFFERENT. Ullr switches between melee and ranged. Hel between healing and damage. Tyr between sustain and damage.
What does Fafnir 'switch' between? Damage and slightly more damage?
I rest by my conclusion: Fafnir's ult is not a stance switch.