"Traxigor is a 17th level Wizard polymorphed into an otter."
I strongly disagree
You can disagree all you like, but that is the history of that particular creature. It isn't a species, but rather a unique individual that wished for the physical form of an otter (or approximately that of an otter; I think he can still talk and use his forepaws as hands and whatnot).
Traxigor is a beast CR 12 with spellcasting. The Polymoprh turn you into a beast with CR equal or lower than your level.
"Plus, such a transformation wouldn't be very useful since Polymorph states that "and it can't speak, cast spells" so... no you can't."
I strongly disagree,
The creature is limited in the
Actions it can perform by the
Nature of its new form, and it can't speak, cast
Spells, or take any other action that requires hands or
Speech.
Traxigor can use hands and speech to cast spells. So, casting is avaiable for this new form.
You see the end of that line: "The creature is limited in the actions it can perform by the nature of its new form,
AND it can't speak, cast spells, or take any action that requires hands or speech." The AND is adding another restriction to the Polymorph form. It means that you are BOTH limited by the nature of your new form AND that you can't speak or cast spells (or use your hands).
Here is that corresponding line from True Polymorph: "The creature is limited in the actions it can perform by the nature of its new form, and it can't speak, cast spells, or take any other action that requires hands or speech,
unless its new form is capable of such actions." Notice how that part is missing from the Polymorph spell? Without that line, you are an otter with some extra (for an otter) hit points.
Do you know what that means? It means a Polymorphed-into-Traxigor character can't cast spells. A True Polymorphed-into-Traxigor character could. Is your Sorcerer casting True Polymorph? No? Too bad; you really otter've thought that one through.
Your character has failed in countless ways and Feeblemind doesn't even work, since Simulacrum's Greater Restoration dispell that

I don't need to repeat everything again. Haha
. But, Not even initiative you rolled, because you aren't involved in combat. HAhaha, a sad death.
You still don't know how D&D initiative works. If you declare a hostile action, initiative is rolled. That's it. It's not about what the target perceives, it's about your action declaration. If it helps you conceptualize it more clearly, think of things that remove surprise (the Alert feat, Foresight) as something like Spidey Sense. If a person isn't surprised (after your hostile action declaration), and if they win initiative then they can take an action, secure in the knowledge that some unseen entity was about to start some hostilities with them. Don't like that? Then stop pretending you are playing (or discussing the play of) 5e D&D.
As to the purported victories of your characters against anyone, they can't have won anything. None of the builds so far, to my knowledge, have been legal, so there was never anyone for the Wizards to fight. (Holy Boi: Two too many spells known; Sparky Boi: One too many spells known; Coffee Boi: One too few "clockwork" spells known at level 1, so one too many spells somewhere else).
As to the subtle spell on Planar Binding stuff, if it is possible to get the spell off subtly (presumably by Wish), then that still doesn't mean that the creature obeys your mental command without twisting it. They might not recognize your face, but they are likely to be hostile to whomever bound them, and so those orders are very likely to be . . . creatively interpreted.
Remember that "imperceptible" is not a term of art. It is a bit of flowery wording with no real weight in the game. The rules bit might be seen as "cannot be counterspelled" and other such things. Plus, spells with a material component aren't even imperceptible, as the Subtle Spell metamagic doesn't remove that. (At least, that's how we play it in my group. Things do what they say, not more and not less, without some rule-of-cool thrown in.)