Okay, feeling a little gaslighted right now so I'll try to summarize in a big hoorah.
The opposition:
It (the infinite rotation)
is not hitting the target with infinite joules of force. It is hitting the target with 8-B joules of force, which then proceed to push on the target in a rotating pattern forever and ever and ever.
The Infinite Rotation is infinite in the sense that it will never end. The force will push on the target with the same amount of force, forever. You can push back, you can add air friction, you can make the energy disperse as heat - it doesn't matter. You will continue to feel 8-B worth of joules pushing on you in a rotating motion, forever.
Like every other use of the word "infinite" in Part 7, the description is clearly using the word infinite in the sense that it's effects will never stop rather than in the sense that the bullets each hit with infinite force. If the description said "a stand ability with never-ending rotational energy", would it be any less accurate to what is actually shown?
My point of view (what I think is the truth):
The infinite rotation shot is hitting the target with infinite joules of force, in other words, it's a high 3-A attack. As a consequence of the energy being bound to an infinite rotational force (aka basically through hax), the target is forced to spin in a rotating pattern forever and ever.
It's infinite both with the amount of energy the attack delivers, and in the sense that the rotation hax will never end.
Why I know it's the truth:
First of all, a half author statement, half in-verse explanation. Before the start of each chapter, Araki puts information regarding the Steel Ball Run universe and phenomenon.
This is what the compendium has to say about ACT4 :
"TUSK - ACT4
With the rotation using the horse's running power, combined with Johnnys Tusk's rotation, a Stand ability with the power of infinite rotational energy. In order to control gravity, that energy pierces through other dimension. (Its damage is also likely infinite and should never end)"
Very clearly it reads "with the power of infinite rotational energy" and "its damage is also likely infinite". The opposition seems to think that the word infinite is being exchanged with the word endless, since it does have two prominent definitions with never ending being one of them.
Let's first acknowledge how the infinite rotation is based on a prominent math concept in Steel Ball Run, the golden rotation/ratio. It's a real world thing but in JoJo it's weaponized to harness more energy via the power of Spin, a science/magic power that allows people to rotate objects.
Knowing that we already know
everything related to the golden ratio is going to be related to math. ACT4 is the embodiement of the infinite rotation, so the two are synonymous in this context. If we know that
the infinite rotation is inspired by and related to math, the definition of the word infinite is probably referring to the mathmatical value, ∞, rather than the unrelated definition meaning "endless". It doesn't make sense to talk about a concept based on math and use the word infinite if you didn't mean ∞.
Second part about that statement,
"(Its damage is also likely infinite and should never end)"
You can see they very clearly made a distinction between it likely being able to perform infinite damage and it forcing the opponent to never stop spinning. Infinite being endless just... doesn't make sense,
"its damage is also likely endless and should never end" is a redundant sentence. Why would it be likely endless if you're just going to say it will never end? This is basic english you guys.
So if I had to rephrase for clarity, it would probably be:
"(The damage performed is likely infinite, and the side-effect of spinning should never end)"
So since everything about the IR is in the context of math, the word infinite is likely referring to the mathmatical value rather than the definition of endless. One of the sentences flat out doesn't make sense when exchanging it for the word endless.
Also, one quick note, "infinite rotational energy" is synonymous with "infinite angular kinetic energy". This means IR has infinite kinetic energy behind the bullet, that's high 3-A.