I don't think they need reinforcements, what they lack in this championship series is the experience. Majority of them have no or 0 championship experience, or even going into the playoffs.
As compare to the Bucks who has suffered in the hands of Toronto and Miami. I think that's enough for them to be battle tested in this year and chase their dreams to win the championship for this season.
Now he got traded from a team which didn't experienced any playoffs for years but have promising players like Ayton and Booker. He literally changed the whole team and its the first time of the Suns to go to the NBA Finals after years of drought.
He has at least 2 years still to get a title and for sure he will stay on the Suns. The only thing that the Suns lacked in the Finals was a big. Saric and Kaminsky are both injured at that time and they don't have any other but Ayton. With how the Suns played in this season, I'm thinking that they will be a team to be reckoned with because they are a strong team. They will come back next season and will enter the playoffs again.
Practically CP3 led the Suns to the finals, Ayton and Booker played very well, the best thing is that they are young and will improve in future, they are like diamonds that will be cut.