It's not he had zero emotions but more they felt limited to stock reactions, he didn't feel driven by his own personality. His reactions to the others felt like a set pile of phrases that never really changed (eg. his 'science is so amazing' reaction to ALL of Clemont's inventions with nothing much else) they didn't really get new sides and bits of development out of him, I didn't feel much sentiment towards them. Most of the companion's sentiment towards him was just idolisation from all of them too, to the point Serena questioned how hallow her relationship with Ash was the one time he acted truly abrasive (this could have been good development, but was swept under the rug instantly afterwards).
It didn't help that XY Ash never really felt out of his comfort zone like the others, he was nearly always in a good position where he could handily solve things with a battle or the plot would break things down for him, I think this is also played into his reactions being limited compared to other series, where the plots and companions usually at least forced a few different emotions and situations him.
Not to mention Ash did still do incredibly stupid things in XY, just they were mandated by plot, so we didn't really get the gratification of them being at his expense or being treated much like a flaw that often (probably the dub's best edit was in the Pokeball factory episode where they have Team Rocket lampshade how exceptionally brainless he and the others had been falling for their trap, I'm sorry but that was well deserved).
The early few episodes of XY may have had some better displays of emotion from Ash, but even then they felt dumbed down from previous series.