The 2020 world champion said Honda “needed a bit more help” after September’s Misano test, at which Marc Marquez admitted the team was “still far” from where it needed to be.
But speaking after Tuesday’s test, Mir was visibly pleased with the progress made, and said the bike “seems to be working better.”
He also revealed it was the "first time I have been able to feel a difference since I arrived" for the 2023 season as Suzuki bowed out of MotoGP.
Mir remarked: "I'm quite happy, it's the first time in a test that they really brought something that worked.
"I felt pretty good all day, it was a challenge, on Friday after the crash I thought I wasn't going to be able to do the test.
"It was hard to improve a little bit every day and it was difficult to get the feeling after not riding during the weekend.
"But I quickly got into the lap times and this bike seems to be working better. We had a very good rhythm in all the rides we did, every time we went out it improved.
"We tried a lot of things and we didn't have time to put the soft tyres on to attack the time, but I'm very happy. The potential is different."
The test marked Honda’s first without Marquez since 2012, as he departed for Gresini Ducati for the 2024 season.
Mir was joined by Luca Marini, who has swapped VR46 for Honda, while his seat at Valentino Rossi’s team was filled by Qatar Grand Prix winner Fabio Di Giannantonio.
The competitiveness of the RC213V has worsened over the last two seasons, with the team’s struggles a key factor in Marquez’s departure.
The factory Honda team’s most recent grand prix podium was at Motegi earlier this year, while its last win came in Emilia Romagna in 2021.
Mir said the new bike’s weight reduction has helped its handling, but said the engine is "not fantastic" and is a key area to improve ahead of February’s Sepang pre-season test.
"It is longer and also weighs less, that's the reality. It's a first step to have a competitive bike, it's still missing but it's a good step, the times were different," the Spaniard explained.
"The track was not very good, in the afternoon there was a moment when there was no wind but just then we were in the box, that's what was missing, to have the track in good conditions for a while and to be able to do laps.
"In the end there were 15 minutes to go, but we didn't need to gamble. I'm happy today.
"The engine is not fantastic, it's not the best they brought, it's one of the things they need to improve for the Sepang test, but I'm happy overall."
He added: "The grip is better, we suffered a lot there and that's a clear improvement. Then also the handling of the bike, it's much easier because it weighs less.
"It has become an easier bike to ride. The character of the engine is a little bit the same and that we have to keep working on.
"When you are already in the times and you see that you only need to improve one or two tenths you are already starting from another point and that makes me very happy."
After the disappointing Misano test, Mir was pleased with Honda's ability to react, and believes it is "just a matter of time" before things improved further.
"It's clear that these people know how to make bikes, I think it's just a matter of time before they bring something that really works and from there to improve," he said.
"The bike I rode today is a good starting point to do good things next year, we need to take another step but seeing what I saw today I'm sure they will."
