In terms of the Celtics winning an NBA championship (not just competing), it seems like a Giannis trade is this teams only hope.
In the current NBA tax climate, the Celtics have 135.3 million in 3 players. They have 107.2 million in two players, and only one being a top 10 talent.
The Celtics lost Kornet & Horford for nothing in free agency, and (essentially) gave away Holiday & Porzingis for nothing.
The Celtics have their own 2026 pick, but it will most likely end up being outside of the lottery.
A trade for Giannis seems the Celtics only viable way of winning a title in the next few seasons.