On #1, it's specifically the TMI comparison in the article that isn't very convincing, because many of the postmortems (though there is some disagreement) conclude that it was somewhat luck that the corium didn't melt through the containment at TMI, due to the specific pattern of melting and cooling. So the fact that it held doesn't tell you what would happen in another incident with much confidence (even if the two designs were the same, which they aren't). There may be other reasons to conclude that breaching containment is unlikely, but the particular argument the article presents isn't a great one.
Comments
On #1, it's specifically the TMI comparison in the article that isn't very convincing, because many of the postmortems (though there is some disagreement) conclude that it was somewhat luck that the corium didn't melt through the containment at TMI, due to the specific pattern of melting and cooling. So the fact that it held doesn't tell you what would happen in another incident with much confidence (even if the two designs were the same, which they aren't). There may be other reasons to conclude that breaching containment is unlikely, but the particular argument the article presents isn't a great one.