He raises some good points.
One thing that has always troubled me about trying to tell the story the way that it’s laid out in the books is some of the ages of the younger characters. This becomes especially hard to do on a TV series. For example, in The Gunslinger, we get flashbacks to young Roland, Cuthbert and Alain going through Gunslinger training. Then, much later in the story, we pick back up with them and get the rest of Roland’s background. Some time passes between both of those moments of young Roland’s life, but not so much that he would look, say, 3-4 years older. Although I suppose the second part of that story (Wizard and Glass) could work if Roland was a bit older.
There’s also Jake. He enters the story in The Gunslinger, and then reappears at the tail end of the second book, and he’s the same age. It’s not as wide a gap as the one between The Gunslinger and Wizard and Glass, but Jake is supposed to be about 12 (if I remember right) and kids at that age begin to age rapidly, so there’s a good chance the actor they cast could look very different by the time they do the second book. I suppose they could alter the story a bit so that it would work if the actor is older, but it still may complicate things (just look at how delays have forced the producers of Stranger Things to have to retool seasons or even recast some roles because the original kids have all grown up). It’s not an impossible task but it does make it difficult.