I personally think most of the issues people point to are fairly surface-level stuff that doesn’t really damage the movie as a whole. A second Death Star makes sense in-universe.
Return of the Jedi is a great movie, but I kind of think this is a stretch. The last one didn’t work, why would a second one with essentially no changes work this time? Palpatine gets a surprise attack on the Rebels I guess, but he still dies, they still lose the Sanctuary Moon, and the loss on Endor doomed the Empire.
Just because your expensive military hardware is destroyed in a battle, you do not simply stop making that hardware. When a country lost a capital warship during the World War I or World War II, they did not just say “oh that did not work, let’s stop building new ones” or “oh that did not work, let’s just stick to building small torpedo boats instead”.
If capital warships were incredibly expensive and had a well known, easily exploitable weak point that leads to total, irreparable destruction, they probably might have said that.
Except that the weak point you refer to was not well known (it took Alliance a great effort to find out about it), and it was not easily exploitable (without a pilot with rare force abilities it was impossible to do it, as clearly shown in the film). And besides, who says they did not fix it for the DS2? The only reason why ships could fly inside it was because it was only 1/4 finished by the time of ROTJ.
Now going to my analogy, unlike DS in Star Wars, real-life incredibly expensive capital warships (i.e., battleships) did actually have several well known, easily exploitable weak points, i.e., against attacks from relatively inexpensive aircraft or torpedo boats. Yet they were still building them for decades after those weak points were evident.