Arsenal are starting to move in the transfer market this season, they are strengthening their team and hope that good things will come to them next season after they failed to win the Premier League this season. Rice Declan is a good player, but I can't say for sure whether he will contribute to the team or vice versa, because he needs an adaptation process and I don't know if it will go smoothly or not.
Arsenal haven't signed any player yet, thus we can't say they are strengthening their team just yet, but i expect them to do so. Declan rice is a good player, but he definitely isn't worth the amount that West Ham value him at, most of these English players are hyped beyond what they actually contribute to the team. I don't even think Arsenal can get Declan Rice with that price tag, there are quite a lot of clubs that are richer than Arsenal, and they'd be willing to pay more money than them to get the English international.