Don’t necessarily agree with this take. Just because Lord and Miller’s high-profile successes have been in the realm of predominantly slapstick self-referential comedy doesn’t necessarily mean they can’t tamp down their comedic sensibilities to fit with a Han Solo film. It does them a disservice as filmmakers to imply that they wouldn’t understand the tone that such a film would require.
The obvious counterpoint would be to refer to the Russo Brothers, who come off of directing not only comedy, but television comedy. Most notably Arrested Development and Community. You could make the same argument against them directing Captain America 2, but the end result would prove you wrong. The Winter Soldier is still one of the best movies Marvel’s ever produced. Yes, it may be a comic book movie, but the gulf of sensibilities between it and the Russo’s typical work is just as wide if not wider as that between Lord and Miller’s work and the Han Solo film.