Arsenal fell behind inside the opening quarter of an hour in Dublin as Kepa Arrizabalaga failed to deal with a corner, allowing Rodrigo Riquelme a simple tap-in, before a loose clearance from the goalkeeper gifted Betis a second through Nelson Deossa.
Christos Tzolis' corner was headed in by Piero Hincapié to give Arsenal hope, but Kai Havertz's misplaced pass allowed Pablo Fornals to restore the two-goal cushion, and the game petered out as Arteta made wholesale changes across the second half.
Asked for his reflections, Arteta pointed to the number of changes his side had made and the gulf between how Arsenal played and how they competed.
"The important part is to win it and we didn't manage to win it, so disappointed obviously for the result," he said.
"It's true we used 25 players, so you need to give a bit of context to the game. In the first half, with more starters, two very different things: how we played and how we competed, because we had some fantastic moments in the time we played.
"We competed especially in and around our box in a number of standards that we are used to, so there are things to improve, some positives to take from the game, and then a bad result sometimes it's good to create even more fire in the belly."
The result came as Arsenal closed in on a £75m deal to sign Bruno Guimaraes from Newcastle United, with the Brazil midfielder set to become Arteta's latest addition following Kepa and Illan Meslier's arrivals in goal.
Arteta refused to be drawn on the Newcastle captain specifically.
"I'm not going to talk about any players who aren't Arsenal players," he said, though he was more forthcoming on the broader picture. "Well, I can tell you at the moment that something happens and we can announce it. I will give you my straight answer."
The champions' pursuit of Vinicius Junior, meanwhile, has hit a snag, with Real Madrid's contract talks with the Brazilian reported to be progressing positively.
Arteta also confirmed 16-year-old academy midfielder Caedach O'Neill had caught his eye during the defeat.
"I've been really impressed with him. What he says, he's really mature and really focused, and he has a tremendous quality to him," he said.
On Christian Norgaard's imminent £7m departure to Everton, Arteta was warm in his assessment: "He played a tremendous role for us. When I brought him here I said that he could be our group player. An incredible capacity to bring people together, to keep the standards high. He had a massive opportunity with a manager and a club that I know really well. We wish him all the best and thank you."
Arteta struck a more sombre tone on Louis Copley's injury: "It doesn't look good, the mechanism is not too positive, the symptoms that he already has either. So let's hope that tomorrow the news are better." On the mood inside a below-par dressing room, he added: "Very upset, given a hard time. They are fuming, but this is good. That's what we need."