Still more expensive to have both rides on the docket for in-season and off-season maintenance, parts, etc. And while wear and tear will still be more than half of what it once was, you only get a half-day's utilization from each attraction when you half-staff them. Not great overall. And I think it's a wash in terms of guest experience; for half the day the popular Baron ride will be shuttered while the tiny swings ride bores kids to death.
Seriously, my kids hated that tiny swings ride, even when they were barely old enough to ride it. Never a crowd. Occasionally a one-cycle line, only because the load/unload was annoyingly slow.
I kind of agree with the general spirit of your "lose two, gain one" point, though. The general metaphorical feel I've had around the park for years is that they're picking rocks out of the water after dropping the water level to the point where a handful stick out. And I do wonder where the water level goes from here. It's just a different operation post-AB.