I think it depends on how you define “developing countries”!
I’m currently in Thailand and I got 6 GB for about $2 total (50 baht for the SIM with 3 GB for 3 days, another 20 baht top up for another 3 GB / 3 days). I did use eSIM for about a month before that though (I just wanted a local number to order some stuff from Lazada).
Another example (also from Southeast Asia, FWIW): Malaysian SIMs are also cheaper, though topping them up is painful so I’d personally stick with an eSIM there.
I find that for light data users (ie. < 5GB), esims are always almost cheaper than local sims, except for maybe in developing countries.