They try changing the female lead to prevent staleness, well look at Brock he is the most stale character on the anime, Team Rocket is less stale than he is. Either give him a goal for each region i.e. GF or PL, but they do not they just make him THERE. HE IS USELESS, HE NEVER DOES ANYTHING, do not say Doc Brock either, that proves Ash will never learn anything. Pachi had the same thing his UberChu had once! Ash should have known this! Ash and Pikachu both "reset" it seems.
Well, I kinda hated "Brock Must Stay" episodes, as the plot of these episodes have bad continuity issues. For example, in Sick Daze, they had Misty performing terribly in regards to cooking, even though she was the one who was able to make the Stun Spore Potion in the Orange Islands, and not to mention, she was most likely the one who helped themselves survive the 13 days in Viridian forest (we know from the first episode that Ash doesn't have the basic survival techniques down.).
In "You Never Can Taillow", Brock returns because Ash can't cook, despite the fact that they didn't need to have Brock cooking in OI or Viridian forest (heck, Brock wasn't even INTRODUCED yet in the latter).
Now, with Doc Brock, you'd think that, what, with Pikachu having gone through a cold, oh, I don't know, THREE TIMES IN HIS CAREER, he would know how to treat Pachirisu (seeing how it's symptoms and organs are similar to Pikachu's), but no.... they just HAD to throw away ALL of that (despite being quite important to the story, with the first cold being the one where Ash caught Muk, the second one being how he first met May, and the third being how he got the Dynamo Badge [albeit undeservingly, but still.].).