Spreadsheets are just a simple tool. Reality and C2C unit upgrades are more complex than they can handle. This does not mean we should change either just for the tool.
Not what I'm advocating. I wanted us to start mapping out the upgrade chains on a spreadsheet. That doesn't mean they should not be allowed to have crossover points, blend points, splits into other lines etc...
If your comment is intended to combat the sense that I'm advocating keeping all units to simple single chains of upgrades and to eliminate crossovers and blends, that's not at all what I have in mind. However we do need to be careful with these so that they don't mess up the AI by inviting units of a particular AI type to upgrade first into a unit with a completely different AI focus, and we do have a lot of points where it currently does, which would be nice to resolve in the process.
As for the graphic, that wasn't at all the point of the discussion. Once you setup units on such a spreadsheet, it becomes the basis for plotting out progressions of all sorts of other tags, such as withdrawal amounts, strengths, movement pts, etc. Just because it's complex doesn't mean that we shouldn't do it and rely on that tool for design. The xml alone makes for a very poor design bible because you cannot get an ease of overview with it. Working with XML alone is like exploring a city on foot where having it all on spreadsheets is like having a map.
You can also more easily spot the direct problems and plan how to address them that we're trying to solve right now, which is that some of the tech rearrangements have created some issues with upgrade paths being lateral or even contradictory.
I also found that there's an issue with having put folk medicine behind soap making when I was playing the game. This sort of thing also becomes more easily discoverable and resolvable once we have the spreadsheets in order.