But Jamie Heaslip inspired a second-half resurgence as Leinster finished 30-18 winners to book their place at BT Murrayfield on Saturday.
"I think Leinster were the better side throughout the 80 minutes," Kiss said.
"They won the crucial 50-50 in the first 20 or 30 minutes that gave them a 13-0 lead.
"As you have seen most of this season the guys were willing to put their hands up and fight their way back in certain situations and going in 13-11 at half-time was a job that was still doable.
"Early in that second half when we did get a bit of momentum we were not just organised enough to create the space we usually do.
"As happens in these types of games the ball goes up the other end of the park and they put another try on.
"That did change the shape of the game a little bit.
"We still did not think it was lost then, but it certainly gave them a bit of momentum in terms of their belief and it made it more difficult for sure.
"Fair play to Leinster, they delivered what we thought they would, and more, we had to be as good as we were last time if not better and I do not think we were.
"That is by my own and the players' admission, they were just better than us."
Kiss assumed his role on a permanent basis in November after ending seven years as assistant coach with the Ireland national team.
And, with the luxury of a pre-season campaign to come, he believes Ulster can come back next term better than ever.
"My message is this is not an ending but a beginning and the things we are trying to do and working hard to do I do think we have the type of players the type of appetite and the talent and the industry to actually go where we would like to go with it," he added.
"It is probably weird, but I am already looking forward to the off-season and getting my teeth into it from the start.
"It has been a little bit tough to come in a third of the way this season as I did. Guys looking at how I wanted to do things, a bit of change management but I cannot fault the group to a man including the staff who worked hard to make sure we can build something."
To buy tickets for the Guinness PRO12 Grand Final click here. Also follow us on Facebook, join the conversation on Twitter, sign up to our YouTube channel for extensive match highlights and sign up for our newsletter for regular updates on the Guinness PRO12.
63x46.png){kind=logo}