The Sixers are signing Montrezl Harrell. He’s pretty good. He really is. He’s a guy Daryl Morey drafted in Houston and later traded to the Clippers in the Chris Paul deal.

He’s also a guy Doc Rivers once infamously overplayed and cost his L.A. team a possible championship in the bubble.

The point of stuff like this isn’t to suggest Harrell can’t help a team. It’s that if he can’t, his coach won’t notice or try something else.

But it’s difficult to just talk about Trez — again, a perfectly fine talent — for these low prices late in free agency.

Because the Sixers still have an important coaching problem. And this signing simply highlights that problem.

Rivers has had this maddening flaw where he locks on to a backup veteran he trusts and he plays that guy throughout the regular season when it may work, and appears to help the team eke out a few extra wins, which carry important weight for the ultimate standings.

But the opportunity cost is he then fails to tinker with lineups that have a better chance of succeeding in the playoffs, and costs his team chances to ramp up promising young players (see Shai Gilgeous-Alexander, Terrence Mann, or Paul Reed).

His need for a trustworthy backup big can even limit his second-best player too, playing a Ben Simmons, James Harden or Tyrese Maxey in so many lineups with a Dwight Howard or DeAndre Jordan.

So the drawbacks are then that Doc doesn’t experiment once he has his guy. Things like more lineup combinations, five-out, all-shooters, or small-ball. He didn’t feel the need to see Danny Green play alongside Matisse Thybulle much even when the defense struggled mightily. He doesn’t tinker enough to find ways to unlock struggling players like when he needs more out of a Simmons or a Harden. Fans begged Doc to stagger Ben’s minutes with Dwight’s, then later Joel’s, and eventually they’d beg him to stagger Embiid’s minutes more with Harden and Maxey’s to get them going amid slumps, but without a washed big on the floor at the same time.

But the need to pencil in a vet Doc trusts to the lineup made many of those needs take second seat. How can I get Ben going when Joel sits if I have to play Dwight Howard no matter what at the same time!? The natural solution is to play Dwight and Ben together for four months!

As if Ben and Dwight weren’t enough, he didn’t feel the need to ramp up Reed the following year once Andre Drummond came to town. He didn’t need to see Reed even after Drummond was gone and it was just DeAndre Jordan there! He openly chastised the suggestion of playing Reed more when asked late in the year, showing how defensive he can be.

We’re talking some comically bad mistakes no NBA 2K player would make, and the Sixers now make them annually. And it hurts them in the playoffs, now annually. If it does again, we can’t continue to blame the coach whose shown us all his cards.

It’s perfectly full-circle that Trez is here, because Doc wouldn’t be in Philly if he hadn’t coached Trez a few years ago.

Kyle Neubeck of PhillyVoice once mused that the Sixers could bring Dwight back as long as they put checks and balances in place to limit Doc’s reliance on him.

We clearly haven’t evolved much since.

So we’re back here again.

Here’s what I wrote when the team signed DeAndre Jordan last winter:

“So we fans should’t be completely ignored when we say things like “let’s at least see how player X looks before deciding to give all the reserve run to DeAndre.” If the Sixers are willing to experiment and DJ wins out, great. As long as it’s a meritocracy and not a gerontocracy, we all win.

When the glass is half full, this is a no brainer, another low-opportunity cost signing, and DJ figures to offer much more than Cauley-Stein, especially if Harden himself endorsed the decision. When the glass if half empty, Doc is going to overplay his guy rather than experiment with playoff viable lineups and it will predictably combust in a couple of months....”

The double edged sword here is that Harrell is leaps and bounds better than Jordan was. He might well be better than Howard or Drummond too. We’ll see. So that’s the good news. The bad news is that it could take away things fans really want to see like Harden or Maxey and four shooters when Embiid sits, or P.J. Tucker at the five, or Paul Reed and Charles Bassey getting true chances, not to mention whatever wing they could have just added instead.

So since Trez is pretty good, maybe this will work out. He has super long arms, he can contest shots, and represents the best lob threat the team has had since it traded for Harden. He raises their floor and may help them escape the regular season grind less scathed. And maybe there’s a trade coming and it’ll all make more sense. Or maybe Doc will completely change his ways and frantically incorporate more modern looks that Steve Kerr, Jason Kidd, Ime Udoka, Taylor Jenkins or Tyronn Lue have recently had success with, who knows?

But sadly, we can’t just talk much about Trez without wondering how much roster control Doc still has, or if this wouldn’t be a purely wonderful signing if they simply had a more adaptive head coach. Doc’s had a Hall of Fame career, but over the last half decade or more he’s had a fatal flaw. And players like Harrell (and Harrell specifically) bring that flaw out when he just can’t quit them no matter the matchup.