You can certainly add any amount of original content (within technical limits) to a freespace page, but I would suggest that there is also value in brevity.
Technically, there is an article size limit on all wikis - the default is about 2MB which is quite a bit of text (without considering formatting overhead it is extremely roughly 1000 letter sized pages of typed content) - I am not sure if that default was edited here on Wikitree.
With that said, for those few people still using low-speed connections (or some mobile devices that have a harder time with large pages) loading a 2MB page can be a painful experience. On Wikipedia the guideline is that articles larger than 200kb should be split into sub-articles if possible.
Interaction wise, consider that many people on average visit a webpage for less than a minute, skim, and move on. I imagine pages on Wikitree get a more time per visit than the average webpage, but there is still a limit on how much info most people will read through, of course also depending on why they arrived at the page, the layout, 'readability', and writing style of the content, etc.
All this said, I do think a well written narrative is generally more valuable than just linking to other sites; for example, a freespace page can be linked to the profile of each individual mentioned, which in addition to allowing you to find out more about the individuals also helps keep of track of which people mentioned do not have profiles yet.