Your list proves that you need a top tier player to win a championship, and that these players almost always drafted in the top 5.
The only way to get a top tier player is by trade, draft, or free agency.
Historically speaking, free agency is not a valid option for the Celtics, so therefore we have to resort to drafting & trades.
A trade for a top tier player would have to include a very high draft pick. Similarly, as your list proves, a draft pick should be top 5 to stand a reasonable chance to become a top tier player.
THEREFORE, the only way the Celtics can acquire a top tier player and contend for a championship is to have a top 5 draft pick (to be used or traded). I don't get how so many people in this thread think that having a draft pick in the 12 to 24 range will somehow eventually lead to a Championship caliber team.