I did not mention it, but I use the whole stack of Ocsigen (from ocsigen-start). Maybe some people are using the term Eliom to talk about ocsigen stack, I am guilty of doing so. I was very little experienced in web development (a bit of js and typescript) when I decided to use it, and I did not try ocaml alternatives so I can not talk about them. I would not have been comfortable with picking and using different libraries, and this standalone framework was perfect to me.
I had to go through a lot of documentation, maybe for a full-time month (going through tutorials too), but I found it quite clear and written with care, so it was ok. I think when one wants to do something quite specific, it is a bit a pain to go through all the docs to catch the logic, because ocsigen does “everything” (including many things I could not imagine possible ^^). Too me, this is a pro when you want to have a lot of options in one tool (client-server app, cross-platform, reactive programming, elm architecture with vdom…) but a con when you have limited needs that you know will cover your project. I think one who learned to use different libraries over times have a lot of options too of course, but the learning path seems less linear.
Ultimately, when you have to decide where to start, I think it depends of your use case and how much you are familiar with some practice of web programming. Hopefully, the community is very helpful in my experience, I am sure we will help you find a tooling set that suites your need or your expectations.
I do not know what most people are doing, but there are definitely serious industrial players using ocsigen (starting from besport), and it is still under development as far as I know, so it is not “old stuff”. Dune is really a great tool, and I personally would prefer ocsigen-start would build with it. However the Makefile is definitely doing the job right, so I understand they currently focus on other challenges they face (I certainly would do the same choice). I hope some day I will have resources to contribute on this
For REPL based programming, I know nothing about it, but as you state ocaml compilation is fast (and even faster with dune :o).
I think ocaml is a really good language for the web. I notice some like there type preserved from database storage to front-end, I agree so much on this! To me, web use cases are vast and different, that is why web stacks are heterogeneous (it is the case in most languages). I think all people here present good stacks that met their need. Hope you will find yours and that you enjoy, in ocaml or another language