My experience tells me that it's both faster and higher quality to do things in small steps than leave it with your "10x engineers" (everybody thinks they are the one, right?) to "just" rewrite from scratch — and I've got plenty of proof in my close-to-20-years of career (I've never seen that go smooth; I've been a part of dozens of iterative "replace large systems" that were pretty uneventful).
As for the "weakest" engineers, even the "strongest" engineers are weak sometimes (bad day, something personal, health issues, sleep deprivation...).
As for the "weakest" engineers, even the "strongest" engineers are weak sometimes (bad day, something personal, health issues, sleep deprivation...).