Their logic is faulty, but opportunity costs are very real and routinely analyzed in many domains, ranging from systems engineering to advertising.
"They could have invested better" - sure, they probably could have. However, there is no reason to believe they -would- have invested in a way that better serves their customers (or whatever 'better' means, that isn't just maintain the status quo), given they never have shown any inkling to do so in the past. Given no proposed catalyst to cause a change on their part, there is no reason to believe they would have changed; ergo, this particular change's leading to 'better' results equals a better outcome than this change not having occurred.