I disagree with you about the comments about the comparisons, but do not wish to seek an argument based on much subjectiveness.
That being said, I do find your comment about 7 seasons being enough for any show and here's why. Wouldn't it depend on the length of the show episodes and how many episodes there were per season? Game of Thrones arguably is on the short-scale when it comes to episodes. It normally has only ten per season, except Seasons 7 & 8, while most dramas are actually 13 episodes per season. There is also the fact if we compare it to network television, which usually has around 20 episodes. That further complicates the argument around 7 Seasons being enough, since at that point they could have double the number of episodes Game of Thrones has. However, I do see your point, as it all depends on the story they are trying to tell and if that particular show appears to be dragging it out for too long. Which could be said with the amount time it takes Dany to get to Westeros.
Obviously everything I'm saying is subjective, and it's largely down to how long something can maintain my interest. But I think there's an argument to be made that every medium has a sweet spot for length. Films for instance, often start to feel 'baggy' as they crawl towards 3 hours. That's not a hard rule, but I think beyond that pacing becomes a concern, and a movie has to work harder to justify the viewer's time.
I actually think much 20 season network TV is too long, and many shows there would be improved with much of the filler chopped out. I loved Breaking Bad for instance, one of my favourite shows ever, but there were certainly points where I thought it could have been trimmed down and got to the point much quicker.
I think in some ways trying to fit book storylines in (which often currently have no canon conclusion) has given GoT a bit of a 'front-heavy' pacing problem, which now contrasts with the 'thinning out' of this run to the end in a slightly unbalanced way. TV usually works best when it's studying characters in-depth, and the breadth of the GoT universe makes it hard to really treat everything and everyone satisfactorily. Despite this awkwardness, it's remained entertaining and intriguing television,for me at least, and given my previously stated lack of patience, I'm just giving credit where I think it's due. Many more years of GoT, and it's hard to see how it wouldn't just become stale. It's time to draw a line as best they can.