With his contract, trading for Jrue Holiday is going to kill our salary cap for the next 3 years. At that point we're either somehow a playoff team or we're rebuilding. So he'd better be the final piece of the puzzle unless you're shedding huge chunks of salary elsewhere (ie unloading LaVine and/or Sabonis) as part of an overall roster churn.
I highly doubt Boston is trading Jrue Holiday for Malik Monk and also throwing in a pick unless it's a useless late second rounder. Boston already has too many guards and Al Horford is reaching retirement age soon so I expect their preference would be to target a frontcourt player.
I believe I already referenced your points 2 and 3 in my post. I agree with these points. If we can find a trade that Boston likes, I'd be happy to have Holiday on board as the tone setter and veteran voice in the locker room. Probably we'd be the ones sending out pick(s) though.
Naji Marshall is a shade under 6'7" and you've got him starting at PF next to Sabonis who is 6'10. I don't think that makes our size problem any better.
As to Holiday being an excellent fit next to LaVine... again this is just 180 degrees from how I see our current situation. I don't think we're trying to build a team around LaVine. Maybe Monte was but he just got fired. And even if we were, you don't bring in a guy who's got 4 or 5 years left in his NBA career and call that a backcourt. Holiday only makes sense as a stop-gap and culture builder while we look for a new PG.
And lastly, who is trading us a star player to get their hands on an overpaid perennial loser with an expiring contract? I guess Monte did that, but there were extenuating circumstances. If we throw in a massive haul of future picks and LaVine's negative value is just there to match salaries you might make a deal but then you're going all-in on a team with a 36 year old PG and a 30 year old undersized center (in 2026) as your foundation? This is how franchises stay bad for decades. We shouldn't fall into the same trap of selling out our future to chase after aging talent with name recognition that sinks multiple franchises every year. Just build a team of young players who fit together and play defense.