Former Red Bull junior Gasly was promoted from Toro Rosso to Red Bull in 2019 after just one full season with the Faenza squad.
But as the team's cars were developed around Max Verstappen's driving style, Gasly struggled to find his groove and he was demoted back to the sister team during the summer break.
Toro Rosso's Albon replaced Gasly, but the Thai driver had even less experience after just 12 grands prix for the B-team and equally struggled to gain a foothold, being replaced at the end of 2020.
Red Bull brought in the much more experienced Perez for 2021, but he too found life hard alongside Verstappen initially before showing improved form last year.
While the Mexican's three wins and one pole in two seasons pale in comparison to Verstappen, Red Bull has at least found a reliable pair of hands that has helped it bank points and finally dethrone Mercedes as the constructors' world champions.
But the benefit of having the 33-year-old's experience in the team has also shown Horner that in hindsight it was probably too early to bring in Gasly and Albon into such a high-pressure environment.
"The key thing in the appointment of Checo was his experience and it had been unfair, perhaps, on the previous two guys to bring them in so soon," Horner said.
"Checo with that experience, he's been through some of the hard knocks with his career to that point and I think what he's brought to us is he's a very rounded guy, he's a great team player.
"He's got a good outlook on the development of the car and he's very easy to work with. That's what all the reasons were for taking him in the first place and he's delivering on that."
Horner conceded being Verstappen's team-mate is a huge challenge for any driver, but feels Perez has risen to it.
Despite a clash in last year's Brazilian Grand Prix, when Verstappen refused to help Perez clinch second in the drivers' standings due to an earlier disagreement, Horner reckons Perez is "mature enough to be able to deal with" being Verstappen's partner.
"It's tough for him having Max Verstappen as your team-mate, I mean, he is setting the barometer in Formula 1 currently," Horner added.
"But Checo is mature enough to be able to deal with that and handle that. And I think that he's looking to continue to evolve and improve his own performance, so it's good to see him looking competitive.
"He won two grands prix last year, he won a grand prix the year before, he was a key part in us and winning the constructors’ world championship."
