The Permanent EXP Share | Bulbagarden
I presume this has to do with "F*** you, got mine" specifically the "I suffered to get to where I am today, so everyone else should suffer to" subset. The idea being that becuase they had to waste time training up their party, that others must as well.
A related issue is that starting with Gen 6, Pokemon difficulty in general had taken a dive and as such people blamed the Exp Share for that (ignoring most other factors, including the free Mega Lucario, and the variety of mons you can get even at route 1).
These other factors are actually related with the former. Part of the difficulty in the earlier games is that Early routes had the diversity of Victorian England and as such were filled with Normal, Bug, Flying, Dark and Water types (if near the sea), a roster that has severe weaknesses that the starter may not compensate for (esp if you picked the Water starter). Assuming you had decided to fill yout party ASAP, you would be left with mons that struggle to keep up outside the starter, have common shared weaknesses and might not be enoguth to contend with the E4 (esp if said E4 wa sSinnoh's, which is not that far from when X and Y were released). If you wanted something that can counter a specific gym's type specialty and said specialty isn't weak to any of those types, then you have to find a nearby mon of the right type and train it up as it would likely be severely underleveled (an extreme case being the Johto games). BW actually srtated to adress the issue by making Audino, Unova's chansey analoge, an omnipresent but uncommon staple of all its area's wild pokemon rosters, which combined with the shaking grass mechanic, made it easy to level grind reltive to the predecessors (esp since it debuted a new EXP system that scaled based on how wide the level gap is, something I don't think the 3DS games had)
Another thing people complain about is affection, for similar reason. It is not QoL but rather another attempt to show the bonds betwixt trainer and mon, but it also made the game easier by basically loading the dice as far as evasion or crits go (and having new effects like a RNG based Sturdy or status purging).
