Not sure what happened here.

Opener: Kxx-A10xxxx-AJx-x
Responder: Axxx-Qxx-Qx-AQxx

USA 2 had an auction I hate. After a 1H opening, looking at three hearts and four spades, Responder bid a silly 1S. This resulted in a heart rebid and a practical 4H. Thus, there was nothing in the way of any communication, at all.

Give Opener the exact same hand, but reverse the black suits. x-A10xxxx-AJx-Kxx. With that hand, the contract seems to turn on a diamond hook and heart cooperating, which is a bad slam. Add one point, though. x-AJ10xxx-AJx-Kxx. Now, the slam is a 75% slam. Really bad to end up in 4H without a clue as to whether this is right or not. The spade bid, if anything, would discourage Opener if he has a stiff, which would not be a bad thing.

So, I dislike the USA 2 sequence.

I liked the start of the Italian sequence. 2C is my view of the right call. Set a GF when you have 3-card support for Opener's major, even with five in the other major, I say. Makes life easier. A common theme. I don't know whether 2C did set a GF, though.

However, a necessary requirement to this making sense is for Opener to not rebid in a 3-card major for some unknown reason. I don't know why Versace rebid 2S. This must mean something in their approach that I do not understand.

The resulting auction was strange to me. A 2NT rebid followed, by Responder. Opener rebid 3H, which I presume to be natural. Responder bid 3S, which might have been a cue or might have been natural. I just cannot follow the sequence:

1H-2C-2S-2NT-3H-3S-4C-4S-5D-5H-6H-6S.

The end was really bad.

If Opener opts to rebid a three-card suit rather than his six-card suit, which might make sense, then 2D stands out. If the sequence is GF, Responder sets trumps (2H), and cuebidding starts. 2NT by Opener (not two of the top three honors) lets Responder know immediately that there is a likely heart loser. He bids 3C anyway, also two of the top three honors. Opener bypasses 3D to deny two top diamond honors, bidding 3H to show one of the top three hearts.

Responder at this point knows that there is likely a diamond problem and a heart problem. However, the proposed hand for a 75% slam still is possible. So, he trudges on with a 3S cue.

Opener, had he held the club King, would be able to cue that card as a courtesy cue.

So, imagine two hands:

x-AJ10xxx-AJx-Kxx
Kxx-A10xxxx-AJx-x

With the former, where slam makes, Opener cues 4C next and could accept a 4D "last train" call because of the stiff spade, great heart secondaries, and diamond Jack.

With the latter, where slam fails, Opener has no serious interest and no cues left, bidding 4H, which is passed.

Thus, the extra space from a 2D call would help tremendously.

Back up, though. If Opener rebids 2H instead, what happens? Now, Responder must bid 3H to set trumps. This allows less room to explore. Opener cues 3S, whether he has the Kxx situation or the stiff. Responder, with only a 14-count, and quacks, bids a courtesy 4C, showing two of the top three clubs.

Back to Opener and the two proposed hands.

With the stiff spade hand (x-AJ10xxx-AJx-Kxx), Opener has a fighting chance. The stiff spade looks nice, the club King looks really nice, and Opener has two Aces. Maybe slam is found, maybe not. But, there is a chance. At least sniffing occurs.

With the actual hand, however, Opener has no interest at this point. A slow spade control, stiff in partner's suit, lousy hearts. A signoff occurs without grief.

In sum, then, I hate the USA 2 sequence. I love the Italian start, but I lost them.