I will agree with this. Mozart was the only composer who instinctively knew how to write for every instrument he used, including voice. Every singer out there will tell you that their favorite composer is Mozart.
As for the list - it's all so subjective. I'd put Strauss, Bruckner, Puccini, Saint-Saens, and a few others ahead of Stravinsky. And then there were the Venetians - Vivialdi, Montiverdi, Galluppi - all could adapt their composing to the room better than Beethoven and Bach could. But, they had a different purpose. I won't argue Verdi at all or to an extent Schubert, but that's my taste.
Really, if you look at this list, it's more a list of composers who changed the game. Each was the initiator of a specific style. That has to be the only reason Wagner made the list. Talk about long-winded.
In that case, could Palestrina be put on the list?