Earlier quoted context omitted.
Being there quick is not useful when you do nothing of value and leave immediately though.
Experience gained in the last 20yr in the middle east (Afghanistan in particular) indicates that what we traditionally consider "fighter" type aircraft are capable of delivering various guided munitions with sufficient accuracy and that time to location is highly important. Having dedicated CAS aircraft is nice and it's probably wise to keep something of that nature in service at all time but it's foolish to pretend…
I would say it is foolish to make such a broad generalization like that a plane being new and designated multirole is enough for it to fill all CAS roles (there's more than 1 type of CAS mission) "with reasonable effectiveness". In the case of F-35 replacing A-10, we know that it won't be able to fill some of those roles.