There's a dataset like that in the demo at https://vimeo.com/manage/videos/553439658 . Ultorg handles larger datasets through a number of strategies: (1) automatic LIMIT clauses with an infinite scroll like mechanism, and with various rules to deal with the nested data structure, (2) a multi-threaded UI that keeps the visual query representation responsive even during long-running queries, (3) automatic cancellation of ongoing queries if the user makes a change, e.g. to add a filter, (4) "frozen" headers and values that makes the data make visual sense even as you scroll down multiple pages, (5) a separate "single-column" form layout type that works well when you have a few grouping fields followed by a long subtable, and a few others.

(Author of Ultorg here.)