I'm curious what shows you're thinking of that started out bad before getting good. I can understand why you'd rather not give examples (presumably because you don't want it to devolve into debates about specific shows), but most of the ones I can think of are older ones when they had a lot more episodes to make and more time to fill.

Maybe something like Star Trek: The Next Generation? Or even stuff like Buffy and The X-Files (which I don't think started out bad but it did take them a season or two to really get their footing).

Generally speaking though I feel like very few shows I've watched in recent years are like this. Due to shorter seasons and more serialized storylines, they usually feel like they've been pretty well thought out beforehand compared to shows from the 90s or early 2000s. Or maybe I'm just not watching those shows.