There's definitely a lot of stuff that's unjustifiably missing from the older games, but even all that isn't enough to get me to play New Leaf over New Horizons. Though admittedly, I am extremely biased towards playing on my TV instead of a handheld, so that's where most of my strong feelings on the topic come from. Even discounting that though, I still feel, despite all that's missing, New Horizons has still made New Leaf completely obsolete.
Oh i didn't stop playing NH actually.
I am playing both at the moment and it is making things more fun because the things that NH lacks, NL has it and vice versa. Although, i am getting a bit of a headache from playing two games at the same time lol
I feel like NL isn't obsolete because it focuses more on relaxing and interacting with your villagers than doing multiple stuff to keep you busy.
Like, in a few days of NL i already visited and got visited more by my villagers, received more requests from them, got more presents like clothes, got asked more questions and saw more unique dialogue than my entire playthrough of New Horizons.
It feels more rewarding to interact with them in New Leaf, sometimes even being required to progress as you cannot get your development permit without getting to know them at least a little bit.
Also, in my opinion, the dialogue feels far more repetitive and humorless in NH. Most of the time it's only a box of dialogue like "i am fishing right now, hope i catch a fish", but it gets worse when u are visited by someone or there is an event going on, because they don't talk about anything else and everybody in your island is saying basically the same thing. It gets a bit better when u get closer to them, but not that much. I also feel like they tried to compensate the villagers' lack of unique dialogue by increasing the amount of text other npc have like Tom Nook and the Dodo, but their speech ends up being quite redundant and devoid of emotion. Like, do i really have to sit through 2 minutes of dialogue every time i want to visit an island?
Now when it comes to relaxation, i feel like NL does a better job too. Like, the fact that the tools don't break every 2 seconds makes for a much more relaxing playthrough where you don't have to go back to your workbench a hundred times just to catch a few fishes or bugs that at the end of the day are barely going to give you any money. There is also a bigger focus on waiting and more stores and upgrades to unlock by simply doing so (though that might change when the new updates come out).
That is not to say that NH doesn't have it's merits. Like, NL's museum pales in comparison, even despite having two more sections at the moment, and it is really annoying not being able to chose where each house is built aswell as being unable to use your furniture outside of home. Not to mention the graphics are way better.