I have seen for myself. I have many of those phones, or had them and passed them on.
I have an A21S here and i've love for you to defend its performance (Not its battery life, but its day to day performance)
I guess I'm still recovering from my Galaxy Ace 2. That thing lagged a lot. Imagine waiting 30-60 seconds for websites to render. And at the time it was "fast". It was certainly faster than Ace, Wildfire, Galaxy W and it was a phone bellow S line, but I had no idea that it would be still slow. Still it was a massive upgrade from Nokia 5230 touch, which had resistive screen (no multitouch), single core 400 MHz CPU. Sammy had dual core 800 MHz Novathor chip. 5230 didn't even have wifi. Anyway, I later went from Ace 2 to Note 3 Neo and it was truly fast phone. It lasted me 5 years. In the last years it was noticeably not fast, but I could get by. I remember it scored 30k points in modern Antutu. It could also run GTA SA passably. A50, which is my current phone, easily beats old Note 3 Neo. With power saving mode it gets over 110k points and it's just quick all around. Low end A series still have something like Snapdragon 439 (A01) and that SoC reaches around 87k points in Antutu, so it's low end today, but it's still quite good. I could get by with low end phone like that today if I needed to and it wouldn't be an awful experience either. Considering that we used to have phones like Galaxy Y, Galaxy Mini, Sony X10 Mini and etc borderline e-waste with calculator CPUs, not enough RAM, barely any storage for anything other than OS, tiny sub 3 inch screens with 240p screens and 3 MP cameras, things have really changed. The only thing that is worse today is that those old phones used to get a lot of love on XDA and had tons of ROMs to try. Galaxy Y was very customizable and you could overclock CPU by 2 times, put Android 4 or maybe Android 5 on it and make memory card to be usable as storage, which would really transform the whole device. Sadly there's nothing you can do about limited RAM, probably battery too (although there used to be those ridiculous obese battery cases), screen, comms and camera (although mods might exist, but hardware is really limiting factor, so I wouldn't expect software to fix that, considering it had reasonably decent camera software stock). Today, you can just buy bottom of the barrel Samsung and it will have reasonably modern Android version, be overall usable, play lower end games, have good camera and some actual storage, not to mention that it won't lag in general usage or with more than 3 homescreens for less money than that old Galaxy Y. The crazy thing is that A01 would be cheaper than Y probably not even adjusted to inflation. I recall that borderline e-waste to be expensive. And not only phones like A01 kinda awesome for their price, but it does run GTA SA well too, it's also close to S6 in performance. All that for 120 USD in 2019 and it wasn't even sold in US or Europe, I have only seen A10 for a while on sale. So what you can actually find and buy is going to be even better than A01, which is great. Considering how much better mid range phones like A52 are, which are like 3+ times faster than A01 are we really in position to complain about their performance? Even A01 runs GTA SA, unfortunately Asphalt 9 kinda runs, but not very well. Still, it's going to run like 90% of games reasonably well. Anything higher end than A01 will run games better and further reduce unrunnable game portion. And that's gaming, which is probably the most resource intensive task that most of people will do, Snapdragon 439 and higher end chips have no reason to lag in everyday tasks, if they lag in that, then it's more likely that poor governor or IO scheduler choice in ROM is used, rather than SoC itself. And this is A01, A52 is times faster than it and will cope even with shitty governor and IO scheduler picks much better. So today, it's not particularly reasonable to think that mid range or even low end phones will be slow or laggy, it's just simply getting rare and more of leftover from past, than something to really think about.
Edit:
I looked at A32 running Asphalt 9 and it runs it really well with high settings, that's very nice and honestly impressive. A21s, unfortunately, struggles in same game at default settings, perhaps lower settings could fix that. So it seems that S32 level phone is good enough even for intensive gaming (I have looked at its performance in COD and PUBG too). Not that it's fun to play games liek that on phone, but the point is that those "cheap" phones perform well enough to run them well.
