To the point of needing to upgrade a position vs adding a player -
Udoka plays an 8-man rotation. A simple breakdown of the current roster by minutes looks like this (note: obviously the minutes will ultimately be different so the minutes flex up or down ~4 min just keeping it simple for this convo):
1/2 = 96 min = Smart/Brogdan/White all at 32
3/4 = 96 min = Tatum/Brown/Grant all at 32
5 = 48 min = TimeLord 32/Horford 16
So if we are healthy and add another player, who's giving up minutes from the top 8?
The next 3 players on the roster are:
Pritchard (back up 1/2)
Gallinari (back up 3/4)
Vet Center yet to be signed (back up 5)
These 3 roster slots would not play on nights we are at full strength and Ime is trying to win. So spending on these roster slots do not help win in the playoffs (barring injury). These slots are to help manage the long season/seeding.
The last spot on the 12 man roster is likely Hauser at this point and he is prob garbage time only.
Spot 13 is Kornet who will likely be active on the nights Horford sits and the Vet Center moves up to back up.
My point is, outside of a backup big, any addition would likely require White or Grant to be moved. I don't think that is likely. So any money being spent is almost certainly on a backup big with a contract that can be moved (like Theis' addition at deadline).
Couple things. Udoka's rotation was 8 players last year. That doesn't mean it will be this year. Second, there is the very strong possibility that the Celtics make a trade not sending out players, just a TPE and a draft pick
I don't disagree that as the roster stands now and assuming everyone is in general, healthy and available (a big IF), our roster/rotation is fine, quite good actually. But based on last season, and every season other than 2020/21, we have mostly played based on a core rotation of:
1 Combo/PG (Smart)
2 G/F Wings (Brown/Tatum)
2 PF/C Bigs (Horford/RWill)
I don't see any reason that we would go away from that. That does not mean we will always play exactly this way, we will play plenty with 2 combo, 2 bigs and 1 wing; or 2 combo, 2 wing, and 1 big. Assuming the same starters (at least at the beginning of the season) that means our regular rotation back ups for each of those categories are (I am excluding the deep bench):
Combo/PG White/Pritchard
G/F Wing Brogdon
PF/C Bigs Gallinari/Grant
That is still 10 deep if you include Pritchard. Our "shallowest" position is the G/F Wing. Brogdon becomes the principal back up but I am not even sure if his natural position is wing. I think he can be fine at wing but to me, another bench wing is a greater need than an insurance big (which I think is what BruceBanner is saying). We are 4 deep at the big position, 3+ deep at the combo slot (Brogdon can play there but probably won't). We are only 3 deep at wing, 2.75 really if you consider that Brogdon is not a natural wing but can play as a wing. As of now, Hauser is our 4th wing.
Not the end of the world, but picture what happens if Brown's wrist is sore and he has to sit out. Suddenly the wing position looks pretty thin. Brogdon starts and Hauser is the first wing off the bench. More likely, Pritchard and White see more minutes but neither of them are really wings. Compare that to our big rotation, say with Horford resting a back to back. We can start Gallinari and bring Grant off the bench. Maybe Kornet gets 10 min if someone is in foul trouble.