It seems likely to me that many of the EO could be only material and not formal heretics.
Ah, here we go. Just watch that video. Do these people have the Catholic faith? They explicitly reject the true rule of faith.
If you do not have the proper formal motive of faith, then you have no supernatural faith ... whether this be lacking by your own fault or by simple absence.
Even if they happen to have some material beliefs in common with Catholics, they hold them with a completely false rule, a non-infallible rule insufficient for supernatural faith.
You are blinded into believing that simply because there's a bigger overlap in the Venn diagram that charts the objective beliefs of the two groups, i.e. because they're closer to us materially than other groups are, that they have the formal motive of supernatural faith. They do not.
That's why a person who denies a single truth of faith becomes a formal heretic ... even if he continues to hold every other truth ... because in doing so he rejects the rule behind them ALL, and the truths he continues to hold materially he does not hold with the proper formal motive. FORMAL vs. MATERIAL heresy have nothing to do with "sincerity".