Miller signed a two-year factory deal with KTM when Ducati elected to move him out of its works team set-up in favour of Enea Bastianini.
The Australian was offered a chance to remain at Ducati, but only on a one-year deal at Pramac.
Miller, who was runner-up in the 2014 Moto3 world championship with KTM, has made an instant impression on the Austrian marque in 2023, having scored two podiums in the opening five rounds of the campaign.
As well as his encouraging results, Miller's development inputs from his five years of experience at Ducati have boosted KTM.
Speaking exclusively to Motorsport.com, Guidotti said: "Jack has brought with him a lot of experience, which was what we needed.
"His indications have given us security and confirmations.
"He offers us a point of view that we didn't have on our bike; the perspective of someone who wasn't familiar with the KTM. It has been very good for us.
"When we signed him, we were very clear with him: we told him we needed his help to give us feedback on the bike, and push us to take a step forward in its development.
"There was a lot of work. He, after learning that Ducati was not counting on him for the factory team, needed to feel important, and that motivated him a lot."
After five rounds, KTM has registered five podiums between Miller and Brad Binder spread across the sprints and the grands prix. The latter sits third in the championship, 13 points behind leader Francesco Bagnaia.
It comes after a low-key winter for KTM in which it did not look hugely competitive throughout testing.
Its form turnaround was instant, however, with both factory KTMs fighting for the podium from the opening round in Portugal in March.
This sudden boost in results has surprised KTM, with Guidotti adding: "It's not that everything went better than we expected; it's that it went faster than we expected.
"Everything responds to the development work we did in Malaysia and Portugal [in winter testing]."
