I'm going to attempt to answer this in a way that is truthful, and accurate, but maybe not exactly what you're looking for.
Please be very mindful of where I say "assuming this definition, then..." On those statements, I am intentionally using that assumption as a logical starting point for assumptions. I am not saying I hold those views, or that I condone or deny them. I am trying very hard to avoid the mines in this minefield
MacArthur's views are not uncommon. The Catholic Church still teaches doctrines that many Evangelical denominations hold to be un-Scriptural, in error, or even according to some views, outright blasphemy. (Note I didn't say "the Catholic Church teaches wrong things" I said "some denominations teach...)
However, it is one thing to say that the Catholic Church teaches things that are "wrong", and quite another to make a blanket statement that Catholics aren't Christians.
Even if you accept the Reformed/evangelical statement that a Christian is defined as someone who has repented of their sins and put their faith in Christ for salvation, and has this been "born again", you still couldn't make the statement that Catholics are not Christians.
According to reformed theology, salvation is an individual thing. Denomination makes no difference. Again assuming the MacAurthur definition of "Christian", the most you can say is "due to the fact that the Church teaches erroneous statements about what it takes to be saved, it's less likely for a Catholic to be saved."