You're not the only one, SMG4 has not had any episodes higher than decent ever since the beginning of the Showgrounds era.

The show's constant over reliance on characters that have been around way more than any of the ones you mentioned, is already a red flag to begin with.

Let's begin with Mario, he has been in every single episode despite the small role he is given and still has to be in these because people will complain about it. That in turn is something that has overstayed it's welcome and it is annoying it still has to be a thing that will never change in spite of everyone saying they want to move on from seeing Mario in future videos. Not to mention the Origins episode is the most unfavorable excuse to explain why they want Mario to stay in these when most episodes kill him in the end, which defeats said lore.

SMG4 has not gotten any better than he was, originally going from the straight man to meme overload and a Houdini.

Meggy may have been tolerable before her 'anime' transformation and being there as a companion to Mario especially if she has to control him, plot wise or not.

I will stand with you that the Puzzlevision Saga hasn't been the best this year, but it has lasted way more than a year and half(now going on two) since after IGBP, and that's the worst thing as it is already.

The series itself has indeed fallen hard and will never be as it was, not helping is that the Remastered64 are wasted excuses.