Plus it has all of the knowledge from past human/computer chess research, experimentation and tuning that's been done in other chess engines since the 70s helping it.
Stockfish would still be an extremely strong engine even without the training. Alphazero couldn’t even move a single piece without having been trained extensively.
http://tests.stockfishchess.org/tests
Plus it has all of the knowledge from past human/computer chess research, experimentation and tuning that's been done in other chess engines since the 70s helping it.