Quoted By:
15 minutes into this movie and I can already see why people hated BW. It is probably the same reason XYfags loathe SM. It is all about audience management and tone. Take the scene where Ash saves to grass deers (Don't know their name, most Gen 5 Mon look average). In the BW he is slipping, making stupid noises and barely holding it together. DP Ash would have pulled off some incredible feat of athleticism, as in the end of Jewel of Life.
DP fans, going into the BW era probably wanted more of the same. Instead they got a dumber Ash with more slapstick and jokes. I presume that is the same reason why BW-era TR is so hated in Japan, the Japanese there prefer the slapstick dumbasses. Which isn't to say there was no humour in DP but it probably wasn't proportional to what then-fans were used to.
Anyway audience management and tone is important. If you set the tone, as say serious, but then deliver something else entirely it is going to put the audience off- especially when they have gotten used to, and fell in love with, the original vision.
I am not sure if I can pinpoint the exact point where they tried to get serious with Ash but, it seems for the past two decades the Pokemon Anime has been swinging wildly between slapstick and serious- and they struggled to find the right balance which pleased everyone. Is he Crayon Shin? Or is he Goku?
Oddly enough BW and SM, the much loathed seasons, feel like a more natural progression for the Pokemon Anime- in tone. Ash was dumb and prone to slapstick in OG, not to mention arrogant. Take away his arrogance, gitgud and you would probably have someone like SM Ash. Slapstick adventures with a decent trainer.
This is probably what people mean when they treat every iteration of Ash differently. Because the tone of the show has kept changing with each series, it feels like the character is different- even though you've been watching 25 years of the same guy. Even DP Ash has his dumb moments (10x10=)