Why were President Ford & Carter considered ineffective leaders? Is the criticism valid/invalid?

I think the statements is more justified with President Carter than with Ford.  Jimmy Carter was an exceptional diplomat and negotiator, with the Camp David Accords and nuclear disarmament as real and lasting achievements during his administration.  Most Presidents get blamed for the economy during their term, and it usually isn't their fault, but Carter was a little timid on dealing with inflation and job creation.  He was a micromanager, handling things that the President shouldn't handle, like assigning parking spots at the White House, and some say he waited far too long to act in the Iranian Hostage Crisis.

Ford on the other hand never ran for President. He was handed a shattered Oval Office by disgraced outgoing President Richard Nixon.  As a member of the same party as Nixon, it was difficult for him to fix the damage.  He pardoned Nixon, perhaps for a valid reason - to protect the Office of President and not Nixon himself - but it sure looked bad to the public who wanted him held accountable.  As if that wasn't enough, Vietnam, Laos and Cambodia fell in one month in 1975, and our long national tragedy in Vietnam appeared pointless, and Ford impotent to do anything about it.  In this case, I feel he was more a victim of circumstance than lack of talent.