It's less about who's the better/younger player and more about fit, imo.
Siakam fits better with this celtics team than Brown does, imo. Here's why:
-If we look at the last 19 NBA champions, none of them have had 2 guys on the same team with 30% usage and under 25% assist rates. Zero, zilch, nada. Siakam is a lower usage, higher assist guy than Brown. This season, Siakam had a career high 24.9% assist rate, which is MUCH higher than both tatum and brown, despite having a MUCH lower usage rate than both tatum and brown
-Siakam being older than Brown is actually a good thing. Again, looking at the last 19 NBA champions, if we look at the 2 best players for each of those teams, the common trend is that they are typically much older than tatum and brown are. During this year's postseason, tatum and brown's average age was 25.5. If we look at the average age of the 2 best players for the previous 19 NBA champions, ALL of them were older than 25.5. If we take the average age of the 2 best players for the past 19 NBA champions, we get 29.4. So ideally, your 2 best players should have an average age of at least 29.4 if you want to win a championship. Or, as close to that 29.4 number as you can get is ideal, if you're under it. But this year, Tatum and brown's average age was just 25.5, and during next year's playoffs, their average age will be just 26.5. However, if you replace Brown with Siakam, the average age during next year's playoffs of Tatum and Siakam is 28. It might not seem like a lot, but going from average age of 26.5 to 28 could end up being a pretty big difference. Especially since the guy we'd be acquiring (Siakam) is not only 3 years older than Brown, but Siakam has actually won an NBA title before - and played a BIG role in winning that title.
-From a positional standpoint, Siakam is the better fit. Instead of having 2 wings (Tatum and Brown) it's a smoother fit to have 1 wing (tatum) paired with someone who plays a different position, like someone who is a PF / small ball C (Siakam). What lineup do play with Tatum and Brown? If you play Brown at the 2 and Tatum at the 3, there's 2 drawbacks with that. One issue, is that there's not enough minutes for all of our other guards (smart, brogdon, white, pritchard). The other issue, is who plays the 4 in that scenario? Last year when we had brown at the 2 and tatum at the 3, it was usually al at the 4, but he's getting too old now. Ideally, at this point in his career, he's coming off the bench - and playing primarily at the 5. Or, we played Grant at the 4, but he's not good enough to start and is also undersized. If we play Brown at the 3 and Tatum at the 4, now we're not big enough - when we played that lineup we usually got killed on the boards and with opponents scoring easily in the paint (especially if our 5 was someone other than Rob). But with Tatum at the 3 and Siakam at the 4, all of those issues go away. You have enough minutes for all of those other guards, you have good size, and you're not having to play as many mins with al or Grant at the 4.
Brown isn't even the better player, IMO. Siakam's BPM over the last 2 years: 3.5, 3.1. Compare that to JB with 2.1 and then 1.3. Siakam has grown quite a bit as a play maker. He's got a much better assist % than JB, while being less ball dominant (much lower usage % than JB).
Siakam takes less ill advised shots, drives into non-existent driving lanes less, makes less bonehead turnovers, less defensive mistakes. Siakam has more size, would give us a better flowing offense and more consistent defense.
Siakam has a much lower 3Pr, which means he settles for threes less and does a better job at taking higher % shots closer to the basket. His 3Pr last 2 years: 18.1% and 21.9%, compared to JB which is 38.1% and 35.2%. So JB's 3Pr is basically DOUBLE siakam's which means the % of JB's shots that are from 3 are basically double what siakam's is. Everyone on here says we need to stop relying so much on the 3 and take it to the basket more - well here ya go!
Lastly, Siakam's FTr is much better than JB's. This celtics team obviously settles for 3's too much, doesn't do a good enough job of attacking the basket and getting higher % shots closer to the rim. FTr is also a good indicator of that. It tells you how frequently a guy is getting himself to the FT line. Last 2 years: Siakm's FTr is 31.4% and then 36.1%, compared to JB with 26.1% and then 24.9%.
Siakam is more durable, too. Over the last 5 seasons, Siakam has played 335 games, to 322 games for JB. If we just look at the past 2 seasons, Siakam has played 69.5 games per season, compared to just 66.5 games per season for JB. And Siakam has been more durable (played in more games) despite the fact that he's played more mins per game than JB, which really shows he's more durable (last 2 years, Siakam averaging like 37 MPG, to just 34 MPG for JB).
Not to mention, Siakam is a better fit from a financial standpoint. JB is due for a supermax contract, which a) he's not worth that type of contract so we'll have 1 of the worst contracts in the league and b) it'll make it very hard to have enough good players around tatum/brown once they're both on a supermax with the new CBA. Meanwhile, if we acquire Siakam, that won't be an issue. A player can only get supermax contract from the team that drafted him. And Siakam did not make all-NBA team this season. So he's not supermax eligible and even if he was, we wouldn't be the team that could offer it to him. So we'd save a ton of $ by only having Siakam on a regular max contract, instead of paying JB a supermax.
