While you can build it that way it is not at all a good way to do it. You lose all the benefits of paging when handling fragmentation - you basically will never be able to shrink the data segment on most practical programs - and therefore never be able to return memory to the operating system.

brk is an ancient holdover from when memory protection was done via segmentation. Paging eliminates the need for this historical misfeature. I'm a bit sad WASM propagated it further into modern systems.