Miller and McIntosh are of the opinion Luke at the end of ROTJ is the same or at least consistent with Luke in Last Jedi. They draw some parallels, specifically highlighting Luke's conduct in his confrontation with Vader and Palpatine in ROTJ and his confrontation of Ren and subsequent retreat to Ahch-To.
First, the comparison is between Luke at the end of ROTJ and AARP Luke on Ahch-To in Last Jedi.
"In one of the best arguments I've seen in support of Skywalker's character in The Last Jedi, Jonathan McIntosh—who runs the YouTube account Pop Culture Detective—explains why Luke's actions track perfectly with who he was at the end of Return of the Jedi."
McIntosh then addresses a misconception of Luke's victorious outcome in his duel with Vader.
McIntosh: "The misreading: Luke Skywalker uses his great warrior skills to defeat Darth Vader. Once he’s proven himself in combat and stands victorious, Luke does the honorable thing by showing mercy and sparing his enemy. Thereby saving himself from corruption and redeeming his father.
McIntosh "What really happened: Luke tries to avoid fighting but gives into anger. As he bests Vader in combat, Luke realizes his great mistake, winning this fight means losing his soul to the Dark Side. The battle itself is corrupting him, understanding this Luke throws away his weapon..
This is significant because Luke beating Vader in combat is explicitly depicted as a moment of weakness NOT strength.
Luke’s arc in the original trilogy ends with him not only refusing to kill the bad guy, but refusing to even fight a worse villain. This is why Luke’s force projection standoff with Kylo in The Last Jedi is so perfect. It's the ultimate expression of everything Luke has learned."
I have some disagreements with McIntosh's characterization of Luke at the end of ROTJ. Luke is contrasted at the end of ROTJ with his father in ROTS, specifically Anakin's defeat of Dooku.
Luke, fueled by his anger, defeats Vader in ROTJ. It is important to observe upon severing Vader's hand, Luke pauses his attack. As in ROTS, upon Anakin's defeat of Dooku, Palpatine tempts Anakin with an invitation to the dark side by telling Anakin to kill his adversary, and in ROTJ, Palpatine brings to Luke's attention how powerful Luke's "hate" has made Luke, tantalizing Luke with the power he can experience with hate, and then extends a dark side invitation by telling Luke to kill his adversary. Unlike Anakin, who submits to the dark side and kills Dooku, Luke refuses, throws away his weapon, and as a result, does not surrender to the dark side like Anakin.
Luke refusing to submit to the dark side was not a "moment of weakness" but one of strength, a strength Anakin did not project when he removed Dooku's head from his shoulders in ROTS. Luke had just experienced the power hate upon vanquishing Vader, but then had the strength to resist the tempting of the dark side by refusing to kill Vader. Throwing away his weapon was a physical manifestation of his refusal to kill Vader and refusing to surrender to his hate and the dark side. That was strength contrasted with Anakin's weakness.
Throwing away his weapon was also a message to Palpatine that he was not going to be bullied and no fear of Palpatine was going to make him act and kill Vader. Luke was sending a message to Palpatine that you can't make me kill Vader, I am throwing away the very weapon I could use to kill him, and I am not afraid of you, as I stand before you, unarmed and in this moment of vulnerability, I am not doing a damn thing you tell me to, to hell with your powers.
That to me was not a weak moment for Luke but a moment of strength.
"This is why Luke’s force projection standoff with Kylo in The Last Jedi is so perfect. It's the ultimate expression of everything Luke has learned."
Is it though? Seems to me Luke's force projection was a result of a verbal admonishment from Yoda, and realizing he was wrong and now wanted to do what he could to rectify the situation. In ROTJ, and its ending, Luke was not a hermit, neither was he someone who believed in being a hermit. He was very much involved in the Rebellion in ROTJ, including up to the end of the movie. The force projection is consistent with Luke realizing his act of retreating to Ahch-To, which is contrary to his conduct during all of ROTJ, was not the correct choice. Hence, he does what he can to assist the Resistance, just as he had aided the Rebellion decades previously.
The force projection with Kylo Ren also reflects Luke's difficulty of confronting family members who have turned to the dark side. He told Obi-wan he could kill his father, and similarly, he found himself incapable of killing his nephew, his sister's son. The force projection to Kylo is consistent with his view, from ROTJ, that killing family is not in his DNA.
Miller, building upon McIntosh's points, concludes by saying:
Skywalker's character tracks with his decision to kill Kylo Ren when he felt him turning to the Dark Side. That, again, was Skywalker realizing he was giving into his fear, and that's why he changed his mind. When he fled to solitude, that was his ultimate act of pacifism, as was his non-violent confrontation with Ren in the conclusion of the film.
McIntosh and Miller's view is the best attempt at reconciling Luke in Ahch-To and ROTJ, although I am not entirely persuaded.