Ha, I was a Domino person for WAY longer than anyone should have been. Even ran a modern SaaS off of it with a React front-end. I KTed it off to a new dev team just last year, believe it or not.
Because you are absolutely correct - while the client side of that platform was a disaster, the underlying database and its built-in everything was a powerhouse. We ran about 50 million daily requests to the databases, and although we did load balance it to multiple data centers, we also tested it successfully all running off a single server.
Not that I recommend it today - too little talent who knows it, too much baggage around the bad UX from people who don't actually know it, the wrong pricing, and while it does scale quite well up to tens of millions of records and requests, it gets complex after that point, requiring integration with external resources to hold indexes, etc, so even if you did scale it to billions, you've lost that "one server to rule them all" concept that made it so easy to work with.
All that being said, the killer feature of it was how baked in auth was - It had groups, roles, and granular security baked into the platform, even down to field-level security and encryption. So anywhere you wanted to write code, you knew exactly who the user was and what access they had. Everything else about that platform is sufficiently replicated in modern frameworks, except for that
To bring this nostalgic review back to the current point, if I wanted to build a low-code system that would truly meet a variety of use cases, that is were I would focus - auth.