With him, Richard Harris, Robbie Coltrane, and Alan Rickman all gone, the only members of the Hogwarts Professor Tontine left are Maggie Smith and Warwick Davis.
Colm Meany is one of the few TNG cast to have an extensive acting career outside of Star Trek. But also had been in more seasons of Trek than most of the other actors on the show.
I've always thought Harry Potter is one of the best cast movies of all time. Michael Gambon had massive shoes to fill with Dumbledore with everyone already having 2 movies under them and him needing to rise to the occasion, and he did. Sad day for sure, those movies had a permanent impact on me.
I generally respect Michael Gambon and am sad to hear of his passing, but personally I thought he was a horrible Dumbledore in comparison to Harris. His general manner was a stark contrast in Prisoner of Azkaban, and his treatment of Harry in Goblet of Fire was very unDumbledore IMO, and whatever might have been excused regarding differences in style was somewhat destroyed when he said he'd never even read the books in prep for the role.
By the final movies I found him passable, and I will go to my grave believing it's because he didn't understand the character well enough for the first couple, and by the end he did.
You don't have to know the source material to absolutely kill a role though.
Source : I know next to nothing about acting but I saw Werner Herzog in "The Mandalorian" and he nailed that role despite allegedly not giving a shit about the universe and not watching a single movie or reading any of the books.
I wouldn't discount Harris' innate advantages there too; he was 10 years older than Gambon, aged more poorly (having been an alcoholic hellraiser in his younger years), and his natural delivery - even when he was much younger - had that sort-of wizened wheezing sound to it; "old and physically frail but with incredible magic power" was sort of baked in even before he added any actual acting to the mix.
But I don't know if there's an alternative who would have been better in that regard; the three I'm aware of them talking about were Christopher Lee, Ian McKellen, and Peter O'Toole, but the latter two would have played him very much like Gambon did, and I'm not sure if Lee could have pulled off "frail" either given his voice + physical stature.