Back then, I worked on an office suite called Enable, specifically on the spreadsheet module. I can confirm that this is what killed us.
And for the time, Enable's ss had some interesting innovation. One was the integration through the whole suite. But most interesting to me, on the ss team, was the 3D nature of the app.
Excel liked to bill itself as 3D, but it's not really: their tabs aren't a true third dimension. But Enable's was, so any range could be specified with a Z-dimension if you chose. This allowed interesting patterns like a report with an XY plane for each month, with the top one being a summary, implemented by summing (or whatever operation is appropriate) that 1x1 cell down through the Z range.
Another contemporary one I liked to play with also claimed to be 3D and wasn't but in an interesting way. Lucid 3D was actually hierarchical, such that any sheet could expose a single value to be consumed by a single cell in a parent container sheet, recursively.
At one point I found it, but since its gotten lost in various Mac transfers so I am not sure it still exists. I do remember it was uncompilable (ThinkC I believe from 1988). If I find it I will put it somewhere and mention it on my blog (https://thecodist.com). I also have the original manual, buried somewhere as well, which would be enough for someone to try recreating the engine).
Still have the code? You should open source it! Probably nothing comes off it, but that's guaranteed to be the outcome of keeping it closed