Tbh he is in the top 5; but that list is in no shape or form the true top 5, IMO.
1. Oblak
2. De Gea
3. Ter Stegen
4. Courtois
5. Neuer
Buffon is a legend but too old to be performing on his former top level. Navas has amazing matches but also quite a few flukes throughout an entire season. Neuer is yet to show his pre-injury form, which is why I would rate Marc higher than him (at the current moment). Courtois is a WC GK, but has declined a bit lately (his best outings was in the other Madrid jersey).