My polite guess is that none of the Indycar/Champcar drivers mentioned could (or is able to) do what Mansell did to win both the F1 championship and the CART/Indy World Series inside 1 year.
Hehe even if the CART/Indy drivers was offered 5 years my guess is that none would even come near. CatsAreTheWorstDogs: comparing F1 drivers with CART/Indy drivers dont often show much superiority for the later part.
I was not a Mansell fan when he came over to Indy Car, but I was at the '93 race at New Hampshire and his duel with Paul Tracy that day was epic. It was about as hard fought an oval race and win that you could ask for at that time. 4 of his 5 wins that season were on ovals, including a 500 miler at Michigan. There is nothing "abysmal" about that.