Machado signed a ten year contract; Harper, a thirteen year one. We could have signed either/both, and they would have been around for the entire length of whatever the next window of competitiveness is.
Meanwhile, the operative word in your second paragraph is, of course, "if". "If" they spend $300Mish. "If" they spend big on the types of players you mentioned, then yes, we can forget the travesty that was this past offseason. But you have to admit, with this organization, that's a big "if" at this point. With history as our guide, the fear is the "spend" will be on a tier of players below the guys you mentioned.