Ash losing to gym leaders a bad thing is too harsh. the only one who doesn't have an excuse so let's ignore Pikachu for now.
Ash has Turtwig, Staravia, Buizel, Chimchar, and Gligar with very little experience compared to the rest of some of his Pokemon.
To say that Turtwig, Staravia, Buizel, Chimchar, and Gligar winning the gym battles easy because he has more experience is rather illogical.
Do you think Cynthia would win against someone's Garchomp or some other raised Pokemon with a newly captured Turtwig that only knows Tackle, Razor Leaf, Synthesis, and Bite? I highly doubt it because that Pokemon needs some experience because who knows how weak it is.
So Ash losing to the gym leaders is not Ash's fault, nor the writers, in fact no one nor anything is to blame.
Also Ash catching all uber cute Pokemon who win easily is just a slap to Ash's other Pokemon who had to earn their supper. Having Turtwig, Staravia, Chimchar, Buizel, and Gligar cream their opponents (gym leaders) simply because Ash is an experienced trainer is very bad horrible writing. Remember most of the Pokemon Ash catches probably have very little experience to begin with. Now if Ash lost to a Sinnoh Gym Leader with some of his experienced Pokemon, or experienced Pokemon in general is bad writing but keep in mind the very little experience Ash's sinnoh Pokemon.
Pros:
+Interesting (fillerish) episodes
+Ash's team and their potential
+Good Gym battles, and excellent Gym Leader screen time
+Better Training
+Better game mechanics and more realism to the games than before
Cons:
-Possible evolution potential wasted (meaning there is good evoultion potential but also there is a possibility it'll get wasted)
-Fans complaining
