I think you're overlooking a bit of Jrue's versatility. He's capable of being a full-time PG, as that's perhaps his most natural position. However, he hasn't played there exclusively. In fact, over the past three years in New Orleans, he's played PG less than 5% of the time. He's played more time at SF (!!!) there than PG. Yes, it was bad coaching, but the guy was a gamer, and was an elite defender even against SFs.
In 2018, he was the SF, with Rondo being the primary PG and Etwaun Moore getting 80 starts at SG (crazy, right?) Then in 2019, he started (at various times) alongside Tim Frazier, Elfrid Payton, and Moore. In 2020, Lonzo Ball came to town.
The Pelicans should be ashamed. They had two legitimate building blocks for a great team in Anthony Davis and Holiday. Both are gifted, two-way players. And yet, the team could never build a team around them, usually adding bad draft picks and journeymen.
This is the two-edged aspect of being versatile. All of this applies to Smart as well. It is great to have a Swiss Army Knife player like Smart, starter-off the bench, defend pretty much any position, PG-SG, whatever.
The problem for Smart, just like Roy described for Holiday, is that when you play the utility role, you are not able to refine a singular role. If Smart is able to play PG and focus on that role, I believe he will improve. He will still have his moments, no doubt, but if that is his role and it is clear right from the first day of preseason, he will be able to better prepare for that role.
Last season, Marcus averaged 1.9 3s on 5.9 attempts. In a week, that is about 6 for 18, 33%. This is below average and below what you would like from a starting PG. If through better shot selection, he is able to eliminate just 2 bad shots a week (two assumed misses), that is 6 for 16 and 37.5%. Or if he continues to take 18 3s but makes 7 instead of 6, that is 39%. These are not unrealistic expected improvements.
Overall, Smart averaged 13 pts, 5 assts, 2 turnovers, pretty much the same the last two seasons. I think he can bump that to 15 pts, 8 assts as a full time PG. If he can provide this with decent efficiency, he will probably be a top 15 PG, maybe top 10 and the right type of PG (not focused on scoring) for this team.