The DOJ was surely going to sue, and most likely win. Adobe killed their own worse product to buy a competitor. Seems like an open and shut case.
Your analysis seems extremely short-sighted.
So you're saying if you try to build a product, fail and want to acquire that product from another company - now that you have 0 competition with that product - that should somehow be illegal? Why exactly?
Also what product did Adobe had that was in direct competition with Figma?