Understood. I too did not like single headers, and I know exactly what you mean. I've split all headers to be as fine grained as possible. I've come to realize, however, that in some cases, this is good! There are cases where, in most uses, you will certainly need all the core functionality anyway that it makes sense to just group them all together. I'm totally fine with a few header files with another forwarding header that groups the core --same thing. What's essential is keeping the core to a minimum.
You can have both, split headers and then aggregate that into bigger headers and then aggregate those aggregations into an #include