As far as I know, he just didn't want people to play the genocide route as their first one, but this idea developed into making the genocide route really bad.
Not only monsters are trying to make you feel bad using questionable morals (monsters killing humans is fine, because they were made that way, but humans killing monsters or even humans for self-protection is not), your friends and lover betrays you, the last boss is most likely unbeatable without cheats, but also you basically can't continue playing and must sacrifice all your progress in the end to start anew.
Okie dokie
Exhibit A:
The demons do try to make you feel bad in genocide, and constantly Kazuya gives justifiable arguments against their attempts at so. Merciless Kazuya and the concept of Genocide's narrative is to be a downward slope of morality, where at the start all of the actions taken are completely justifiable if a little extreme. It starts reaching the point where fellow humans are killed(which is a crime, by the way) and eventually the murder of a loved one who had literally not threatened him in anyway at that point. If the intention was to make you feel bad for killing killers, the game would never have Kazuya argue back, he would just be all evil and edgy from the start. But he's not, he makes sense at the start, scaringly so.
Exhibit B:
Betray? They think something is really wrong with their friend, and they take rash actions to deal with whatever has happened, are they reckless actions? Sure, definitely. Though Yuuma shows regrets in these actions, and we know with the context of other routes that Reina knows EXACTLY what's wrong with Kazuya. Yet instead of just trying to kill him, she takes this less lethal route. So calling it a betrayal when she used to literally be the Thunder of God is a stretch.
Exhibit C:
Its not, Hyakki is beatable, Hyakki is the only enemy in the entire game with a weakness to Bleeding, a debuff that can only be procced by two weapons in the entire game. Both of which are obtained in the first chapter of Genocide, with one being the FIRST genocide exclusive equipment obtained. Even with the Hyakki Buff, this weakness was kept in. And if you think its stupid that the solution is one specific weapon, this is a meta-game, experimenting with shit is kind of the point. Not to mention you CAN beat her without this, though the alternative is just time consuming.
Exhibit D:
You don't have to sacrifice any progress, just reopen the game a few times. Directly paralleling Undertale's own Genocide End and similarily having small eerie changes mirroring how Genocide permanently affects your file in Undertale.
Overall, if Alan hated the Genocide Route, he could've removed it, he could've never added it. The reason he made the route inaccessible on first run is because that was always the intent. Neutral is meant to act as a basis for the player's judgements on everything, and Genocide is a route that requires deliberate decisions that literally shouldn't happen naturally on a first run unless you deliberately enter the game to do genocide. Which is all this update changed.
Yep, even a jab at genocide players in the Ex stages.
Im not even going to begin to get into this, but theres already been thorough discussion on why this isn't a jab.
Alan cant even defend himself or speak on his own behalf because everytime he goes on a forum he gets harassed by his western audience. Even if you dislike a game dev's decisions, no need to be a dick about it.