So I think most people are not against EENS. The opinion of Bishop Williamson was for example: If they are in x religion, but in "good faith", god may enlighten them at the moment of their death and they will be saved AS catholics (not necessarily my opinion).
Yes, the phrase "as catholics" is the key to avoiding heresy.
If one says the following, they are a (material) heretic, because their description is a denial of dogma:
a. God can save/enlighten a muslim on his deathbed.
b. God can save non-catholics who are "of good faith".
c. God can save non-cathoics who are "sincere" and who desire "to do what God wills".
The problem with the above is that it gives the impression that religion doesn't matter. This denies EENS and it denies the entire PURPOSE of Christ starting His Church.
The proper, catholic, doctrinal way to explain the above scenarios is:
a. God can save/enlighten a muslim
to convert to catholicism on his deathbed.
b. God can
convert non-catholics
to catholicism who are "of good faith".
c. God can
convert non-catholics who are "sincere" and who desire "to do what God wills".
The key phrase is "convert to catholicism". If you leave this part out, you are a heretic, by definition. The doctrine of EENS
requires conversion to catholicism, which is the only way to heaven.
So in saying "God can save a muslim" you are speaking contradiction. God only saves Catholics. It should be said, "God can save a muslim by giving him the graces to convert to Catholicism". This isn't semantics. This is very precise and important theology.