Even if you're not including Irving, Hayward, or Horford in a deal for Leonard, making a trade for him essentially means you're losing one of those three guys, because of the impossibility of having four max players on your roster without hitting the luxury tax year after year.
The other problem with trading for him is that it throws off the positional balancing of your roster. If you include Brown you lose someone who can defend 2s, for instance. If you include Kyrie than you still need to find a PG, and would need to find space to start Brown, Leonard, Hayward, Horford, and Tatum. Honestly he only way it would work is if you traded either Tatum or Hayward for him, and I don't see the organization parting with either.