Assuming S and T....NO signs Lonzo Ball to 3 yr/$20m/$60m or 4 yr/$20m/$80m.
I would involve Thompson, Smart, and even a pick (preferably a second-round pick, but this team is young enough to part with another late 1st round pick if necessary) in some type of trade to acquire Ball and reduce payroll to sign Fournier.
With R.Williams, A. Horford, and now M. Brown, Thompson is not needed.
I am a big Smart fan as I appreciate his defense, first to the floor, take a charge, style of play. I just believe a pass-first PG, who is a better shooter than Smart, and a good defender is better for a team that is looking to build around JB and JT.
Ball, Fournier, Brown, Tatum, Williams is a better team than last year's team or even a team with Marcus Smart at the 1.
I keep coming back to Ball as I don't believe there is a better PG for THIS team who can be acquired at a reasonable price via FA, using TPE, etc that won't cost you more than Smart and Thompson (e.g. Lillard, Paul, et al will have high salaries or require JB/RW). Guys like Westbrook and even Beal will only take shots away from JB and JT. I'd rather keep Smart and have PP as the backup than pick up an average veteran PG just to use the TPE to address the PG position.
A 2021 team of Ball, Fournier, Brown, Tatum, Williams can only get better in 2022 when Big Al's contract is significantly lower/gone and can be used to strengthen the center position and/or bench depending on R.Wiliams ability to stay healthy.