He has played in the premier league before but didn't find success although that's before he became this inform striker scoring lots of goals. When he played he used to be a bench warmer for Brighton but at Arsenal, he's coming into the starting 11 immediately and that's going to give him more opportunities to display his ability. I do think he's a quality player and he's going to prove it regardless of him now playing in a tougher league. His team mates are going to help him alot and Arsenal will become more dangerous in their attack with his addition. Saka now has a someone he can be giving lots of assists.
Time will tell if he really is worth the hype and praises. He has to do exceptionally well when given a chance and also hope to stay fit. You know how injuries ruin player form and careers. A good example to look at is Jesus. When he had just signed for Arsenal and started scoring goals for fun, every one thought it was going to be a very bright career for him at The Emirates until injuries happened.