I wouldn't argue that Danny shouldn't have made the rule because of the outcome, since there very well could have been other teams that for a slightly higher price would have obliged Cleveland anyway.
But even if Riley had managed to extend the Window in Miami for another year or two, I don't think that compares to what Cleveland has, potentially, put together. Really, it makes sense, with Cleveland having got three of the last four #1 picks, that they'd be able to put together something astounding. Add in that they're LeBron's home town and it's not surprising if they have built what could be a monster team for the next 15 years.
The Cavs probably still need another major piece--whether it's Love or someone else--to get there next year or next. (As James has acknowledged.) They still need healthy young defense in the middle and bad management can spoil just about any advantage.
But with all those assets, merely competent management should be able to cash in for years to come if the key players stay healthy and reach even close to their full potential.