If nothing else, the Miami Heat have shown an ability to move forward from their most recent championship era. The Boston Celtics? Not so much.

Given the forum Monday of TNT’s “Area 21” studio to reflect on their 2008 NBA championship and the ensuing breakup that included Ray Allen leaving to pursue what turned into a 2013 title with the Heat, Allen’s former teammates eviscerated the 3-point legend.

On a reunion panel that included TNT regular Kevin Garnett as well as former 2008 championship Celtics Paul Pierce, Rajon Rondo, Kendrick Perkins and Glen “Big Baby” Davis, the five addressed the decision not to include Allen in their plans for a 10-year championship reunion.

“It almost felt like you’re married, and you come home and the wife and the kids and the clothes and everything is out the house, you didn’t get a note or nothing,” Pierce said of Allen’s decision to spurn a larger contract from the Celtics. Allen instead joined LeBron James, Dwyane Wade and Chris Bosh with the Heat only weeks after the Heat ousted the Celtics from the playoffs.

“You didn’t get an Instagram or tweet or nothing. They just gone. Like, man, that’s wrong.”

The focus of the panel was that the Celtics were still built to contend, having grown particularly close amid the playoff struggles that followed that 2008 title, stressing Allen did not consult teammates about departing.

“People don’t understand that this is real life for us,” Garnett said. “The situation with Ray is very sensitive. And I think that when we all talked about doing this reunion tour, we were talking about guys we consider loyal and part of this group.

“When Ray decided to go to the Heat, I felt like he moved on. And he went to pursue another ring, and he got another ring. Shout to him. And that’s it. It wasn’t no other Wizards. It wasn’t no other Spurs. It wasn’t no other Heat. It was all Celtics invited to this.”

Garnett since went on to play with the Brooklyn Nets and Minnesota Timberwolves; Pierce with the Nets, Washington Wizards and Los Angeles Clippers; Davis with the Orlando Magic and Clippers; and Rondo with the Dallas Mavericks, Sacramento Kings and now, as the lone remaining active member of the group, with the Bulls. The contention is those moves and trades were precipitated by Allen starting the Celts’ breakout.

While former Celtics and current Clippers coach Doc Rivers joined the five players on a long-distance hookup to discuss their time together, he wasn’t part of the discussion about Allen. Rivers had reduced Allen’s role in favor of emerging guard Avery Bradley before Allen left.

“I don’t know how his relationship was with Doc – it was kind of souring at the time because Avery was getting more minutes – so I can understand all that,” Pierce said. “But I just felt like we should have had a conversation. I think it would have settled over a bit more. I don’t think we would have been as salty.

“Even though it was Miami … we hated Miami, and that was our rival we going at it with them, LeBron, all of them – I just think if we had all kind of talked about it, it would have been a little different than it is now.”

Allen has largely remained out of the fray, except for a Facebook post Tuesday showing a photo of him tangling with Rondo during a game and the words: “The power to push limits.” Mostly, Allen has continued with post-basketball pursuits, including his organic restaurant in Miami and his role on the board of the U.S. Holocaust Memorial Museum in Washington, recently chronicling on social media his trip to a Nazi death camp with a poignant essay on Instagram.

Davis reflected on how Allen’s departure played out.

“When you build a strong relationship with a group of guys and it’s bigger than self, meaning that the fact that it’s bigger than self, what we did will always stick with us,” he said. “And you owe us at least, ‘Hey, bro, I’m outta here.’ Or, ‘Hey, I’m on to the next.’ Me and (Perkins) had to leave on our own. We didn’t want to leave but had to leave.

“I would say, ‘Hey, know that it’s over with here first before you go over there and jump on the bandwagon, ring-hopping and doing and all that.’ I understand you want to win a ring, but we still believed in ourselves and we still believed we could win.”

Perkins said the next step belongs to Allen, but the Celtics’ front office said Allen will be invited to the team’s 10-year championship anniversary commemoration next season.

“Who’s going to break the ice? And at this point in time, I don’t think it’s on nobody on here to break the ice,” Perkins said. “I actually think it’s on Ray to break the ice. If Ray wants to make amends with anybody up here, whatever the case, I think it’s on him to reach out.”

Despite the rhetoric, Garnett said, “We have no ill will to Ray.”