that is certainly in the realm of “unusable” 
Unfortunately Logseq has a performance issue with large pages right now and although nothing can be done about that until the devs improve the performance, there are ways to work around that.
For example if the page has multiple sections, split these sections into pages and use namespace to connect them.
For if it’s a large page, when editing zooming in that section.
@cannibalox had good tips for these:
Logseq performance has improved quite a bit since then but it’s still a pain point :’(