Cullen's young guns show how to unpick Lam's locks
So it's advantage Munster and Leinster as thoughts turn to the ultimate challenge in Chicago in four days' time.
That said, with two rounds of Pro12 games to be played while the national elite are away on Test duty, opportunity knocks for fringe players to make a mark with their provinces.
There's no doubt that in times past Connacht benefited from having minimal player involvement on Test days.
They are not unduly stretched as things stand either, with just Finlay Bealham, Ultan Dillane and Kieran Marmion in Joe Schmidt's original squad of 34, but that will change as Tiernan O'Halloran, among others, should be pushing for a place in the match-day squad, and even the starting XV.
While Leo Cullen may be handing over 16 of his tried and trusted to Joe Schmidt this month, Leinster's strength in depth is the envy of the other provinces.
On Saturday at the RDS they showed the power of clever thinking against Connacht. The lessons from the Pro12 final in May were clearly learned as they squeezed Connacht tight once they got to the tempo of Pat Lam's system about 15 minutes in.
Call it Leinster's version of the full-court press - certainly it bore strong resemblance to the saucer defence of old, with shooters taking effective gambles at various stages in the outside channels.
As a result, the team without the ball dictated the tempo much more effectively than the team with it - and Connacht normally do that better than anyone.
I don't want to be unkind here because I am 100pc an advocate of the Connacht style of rugby. I love it. However, the key linking bits in the Pro12-winning system - lock (Aly Muldowney) and out-half (AJ MacGinty) - have yet to be replaced to the same effect.
The upshot is that when a smart coaching unit cottons on (and don't underestimate Stuart Lancaster's role in that) then with sensible line-speed aligned to clever defensive decision-making further out, Connacht's game-plan can be upset.
Ultimately, it was the team that wanted it more that took the spoils.
Leinster may not be the finished article, but under Cullen's steady hand - and willingness to trust in others - a slow but very definite process of rebuilding is taking place.
And the talent coming through the excellent underage system in Leinster is Halloween scary.
On Saturday we got a look at that burgeoning talent built on an experienced front-row platform of Cian Healy, Sean Cronin and Mike Ross.
When Sean O'Brien took his leave after 60-plus effective minutes, the back-row of Dan Leavy at No 6, Josh van der Flier at No 7 and Jack Conan in between was surely the quickest ever to pack down in blue.
The backline oozed youthful exuberance. It was a try-scoring night to remember for Adam Byrne and Barry Daly, while Rory O'Loughlin's unselfish defensive work stood out.
At the Kingspan Stadium, meanwhile, Ulster lost their way. In contrast to Leinster they are struggling for strength in depth, particularly up front, with Nick Williams proving as big a loss as I expected him to be.
They have without doubt the most talented set of backs in the country, with a dozen top-class players, although they would struggle to cope without Ruan Pienaar or Paddy Jackson.
Here again immense credit goes to Rassie Erasmus and Munster. This was typical away-day poaching of the Axel Foley era. He would have been mighty proud of the manner in which Munster dug this one out.
This was a win built on physical and moral courage, epitomised by Rory Scannell, who has really impressed since the Munster midfield was outperformed so convincingly at the Aviva a few weeks ago.
Along with Jaco Taute and Tyler Bleyendaal (absent on this occasion) there is promise in the area that had been of most concern for Erasmus.
I like the idea of a left-footed centre alongside a predominantly right-sided out-half, but the younger of the Scannell brothers has a space-creating step worth its weight in gold in the modern claustrophobic midfield.
His late drop-goal reminded me of Ronan O'Gara. There's no finer compliment I can pay.
Farewell to schools great Kevin Kelleher
Alas it was another sad weekend for Irish rugby with the news coming through of Kevin Kelleher's passing. Kevin was honorary secretary to the schools section of the Leinster Branch for over 50 years.
Along with fellow Lansdowne stalwart Caleb Powell, he guided the underage game so well. There was never a problem that couldn't be solved.
The former St Conleth's College headmaster was also a former international referee - and one of the best at that. He oversaw 23 internationals, with his sending-off of legendary All Black Colin Meads at Murrayfield in 1967 his most famous act.
It was the antithesis of everything Kevin stood for, but on that occasion he felt he had no option. The Kiwi icon and the Dublin headmaster went on to become lifelong friends.
We shared the view that referees were becoming much too important as the game evolved through professionalism.
The stance Kevin took was that referees should look, if at all possible, for a reason not to blow the whistle. He was a firm believer in referees interpreting laws for the benefit of the players - always the spirit and seldom the letter.
He joins fellow great administrators Valerie Keogh and Ann McInerney in that great rugby office in the sky.
Ar Dheis De go raibh a anam dilis.