The European champions finally put their stuttering start to the season behind them with 40 minutes of ruthless execution that would have pleased Robespierre against a team who resembled Marie Antoinette.
They came within three points of their own highest score in a Pro12 game and eight points of Ulster's all-time record set against Caerphilly in 2002.
They had the bonus point secured within 26 minutes, scored an incredible nine tries from eight different players and all against a team that included six Wales World Cup semi-finalists and Grand Slam winners, among them the man many are tipping to lead the Lions, Sam Warburton.
Then the Leinster captain shattered any illusions about what had transpired. "We played with good intensity and good tempo, but, if I'm being honest, they were pretty soft in the tackle," he admitted. "Guys still have to score the tries, I guess.
"I thought we showed better intensity than in the last few weeks, particularly in first 40.
"It is good to see guys enjoying themselves and showing a bit more intent. It was nice to get a few tries on the board, that's the kind of rugby we want to play."
It was an indictment of this competition so vociferously defended by Eoin Reddan in the build-up.
More than 17,000 were in attendance for a clash between two sets of blue-chip players, but the visitors barely showed up.
Their international stars will don red jerseys next month and assume another identity. It remains baffling.
In truth, the Leinster faithful won't have cared. Having watched their side struggle in the Heineken Cup against Exeter Chiefs and Scarlets, and having lost Rob Kearney and Isa Nacewa to injury last week, there was relief around Dublin 4 at the freedrom with which the men in blue played.
The problem for them, and Joe Schmidt, is that having seen their team click so well they now lose the majority to the Ireland set-up. Who knows what condition they'll come back in after gruelling games against South Africa, Fiji and Argentina.
For the watching Gert Smal, there were plenty of positives to report. The newly all-Irish front-row obliterated their Welsh opponents for the second week in succession, while Jamie Heaslip got two tries in further evidence of a return to form in Lions year.
Jonathan Sexton played well, only missing kicks when they ceased to be relevant and showing confidence with an audacious cross-kick from his own five-metre line, while Gordon D'Arcy, Fergus McFadden and Brian O'Driscoll showed signs of real form.
It was the minute leading up to the Ireland captain's injury that demonstrated why the severity of his ankle sprain will prey on the minds of most in the coming days.
The 33-year-old left two Cardiff defenders for dead with a trademark step before being hauled down short. He dusted himself down one phase later to take Sexton's pass at his bootlaces, brush Alex Cuthbert aside and offload for Kevin McLaughlin to send Heaslip over for Leinster's third try.
He tried to play on, but his sprained ankle was too painful and he was replaced by Brendan Macken. It will matter to Ireland, but the province didn't seem to mind as Dave Kearney marked his return from injury with the bonus-point try.
Kearney got the ball rolling on his return, exploiting the porous visiting defence to create a try for Richardt Strauss after three minutes, before Sexton and McFadden combined to send Ian Madigan over for his 12th Leinster try.
Having scored just one try in their Heineken Cup games, they went on to score another two before half-time as Heaslip got his second and Cian Healy crossed.
After huffing and puffing for much of the season, Leinster finally stumbled upon a compliant victim. "Our execution was really satisfying," Schmidt said. "I was delighted with our defensive display against Scarlets last week, but to be able to put that together, probably for the first time this year apart from the first 50 minutes against Munster, they're probably the best two halves of attacking footy we've put together this year."
Cullen agreed, saying: "There were aspects that were pleasing, we have come up against some good teams in the last few weeks and I don't think we've been firing on all cylinders.
"We started the season dealing with a lot of pressure and, for whatever reason, it hasn't quite clicked for us. But that was one of those 40s, after that we got a bit disjointed after a lot of changes. We'll take the win and keep going."
After the break, Leinster lost their flow, but the impressive Jordi Murphy scored within two minutes of the restart and Damian Browne and Fionn Carr also scored off the bench.
Cuthbert, Leigh Halfpenny and Tom James did get tries for the visitors, but a try bonus would have been far more than they deserved.
The problem for Leinster is that, having hit such a high, they now go to the Ospreys without 10 of their starting line-up. "We have got a different challenge coming up in the next couple of weeks," Cullen said.
"We had a very disjointed start, allied with injuries with guys coming back at different times as well. It is hard to build momentum, but it is something we have had to deal with over the last few years so we should be used to it.
"Slowly but surely, there are a few guys coming back from injury and that adds to it as well. Rhys Ruddock and Dave Kearney came back tonight and I thought they did really well and hopefully we'll have a few more in the next few weeks."
The Ospreys are next up, but the real focus shifts to the national set-up. As long as O'Driscoll can recover, then there are reasons to be cheerful on this evidence.
Leinster -- I Madigan; D Kearney, B O'Driscoll (B Macken 23), G D'Arcy (F Carr 53), F McFadden; J Sexton, E Reddan; C Healy (H van der Merwe 49), R Strauss (S Cronin 47), M Ross (J Hagan 55), L Cullen (capt) (D Browne ht), D Toner, K McLaughlin (R Ruddock 49), J Murphy (I Boss 66), J Heaslip.
Cardiff -- L Halfpenny; A Cuthbert, D Hewitt, J Roberts, T James (T Williams 66); J Tovey, L Williams (L Jones 57); T Filise, M Breeze (R williams 57), S Andrews (yc 27-37), B Davies (L Reed 49), J Down, J Navidi, S Warburton (R Copeland 49), A Pretorius.
Ref -- I Davies (Wales).