Is this design considered problematic? It really is just Disruptive Student with Unbound, a more color-restrictive cost, and a slightly higher toughness. Much like Disruptive Student, I can see there being a concern that being able to potentially perpetually counter spells is a problem.

I don't think this is a very fun effect to have. I don't mind the idea of on board repeatable counters, but only if the usage is somewhat variable- otherwise things can get too degenerate. This is quite consistent though, even with the soft counter element. Something to try is having you tap multiple creatures for the cost, such that you won't always be able to use the effect. I like how that synergises with other unbound creatures.

My suggestion is then to make it a 1/3 and change the second ability to ", Tap two other untapped creatures you control: Counter target spell unless its controller pays ".

That's a pretty good idea.

This card seemed to have gotten skipped over for blue unbound slot. But I prefer it by far to, say, Coatl of Free Winds.

Really would like for this card to make it in, but two other cards were put in the Unbound slots first.

The problem I have with cards like these is that they're either to weak to play or to annoying to play against. Out of all the unbound cards in blue this is my least favourite just because it can easily make games not fun for players.

I guess I kind of figured that requiring you to tap two creatures balanced the card out.

The way I see it if you have this card without the other two cards to tap, its just a bad creature with unbound. If you do then it becomes a countering machine. Either way one player is being made to feel bad, either you for playing a 1/3 with unbound for 3 or your opponent because everything they cast can effectivly costs 2 more.