No, that part of the reason for Heras' poor performance in 04 and 05 TdF could possibly be, at least according to Heras and Saiz, that Heras could be a better rider during his second Grand Tour of a given calendar year (as in the Vuelta for his historical TdF-Vuelta combo) than during his first Grand Tour of a given year (as in the TdF for his historical TdF-Vuelta combo).
Therefore, if Heras' combo became (whether he tried for all three Grand Tours or not) possibly Giro-TdF, then the TdF would be his second Grand Tour in a given calendar year and he might do better.
Therefore, if Heras' combo became (whether he tried for all three Grand Tours or not) possibly Giro-TdF, then the TdF would be his second Grand Tour in a given calendar year and he might do better.