Chelsea needed Sterling. I said last season that I thought they were missing a Hazard type player, because they had a lot of very good footballers but they lacked that player to cause chaos by beating players in the attacking third. Sterling will improve them a lot. They're still miles better than us right now. Their quality in attack is better than ours by far. Their midfield is lightyears ahead - Kante, Kovacic, Jorginho...and that's just three of them. Their depth players would probably get games for us. In attack they have quite a few good options, though they lack a true goalscorer. I expect them to add to this as the window goes on. I do rate Broja though, and it will be interesting to see how he does for them if given a chance. Defensively they have very good fullbacks, Koulibaly who should be a good addition. They need CBs still, though if I remember correctly, their younger CBs did a good job towards the end of the season.
Regarding Arsenal, the question was who is better right now. Not what they have/will achieve/win. Because neither us nor them will probably win anything this season. But they have proven last season that they are better right now. Them being a young squad is important because it is clear to everybody that these young players are improving quickly and have made them a better team. Jesus is better than Auba and Lacazette, both of whom were really poor at times in the last 2 years for Arsenal. Auba looked lazy whenever I watched them and let the rest of their hard-working side down. Jesus has more to his game right now than either of them. He's a player that never looked out of place at City, yet they upgraded and Arsenal saw the opportunity to sign a player that, really, didn't need to drop down the table to find a club. His signing was a coup for them. Saying their players will cause unrest is speculative at best. They found ways to rotate players last season.