I do agree with this and essentially that was my perception of the system. I think the counter argument that opposes this idea is they (as in the people who argue against this) believes this is double dipping. If I'm paying the Sub, I should have access to everything regardless. Again like how you say it, they did provide the stipend every month so you can just get the power for "free" (technically you paid 15 dollars a month and if I remembered, it only took 2 month of saved stipend to get a "premium power"
I considered a religious argument of sorts, which is to say it was an axiomatic preference, which is fine. Some people like wings, some hate hats, some are uncomfortable with ala carte gaming. You can't argue preference. But some tried to justify that preference on objective grounds, which were generally disprovable. Some claimed subscribers were in some way "penalized" under Freedom by having things they would have gotten anyway require extra cash. Several careful analyses showed that the amount of new content subscribers got included in their subscription post-Freedom was equal to or greater than what subscribers averaged getting prior to Freedom which meant the revenue from Freedom was a rising tide lifting all boats: even players that subscribed but did not buy a single thing from the store benefitted indirectly through more content being available. Some tried to construct more elaborate arguments attempting to show that subscribers were in some way subsidizing the costs of supporting the free players, and thus it was logically deducible that subscribers were getting less resources than before. All of those fell apart under careful review.
Although it probably isn't a popular notion nowadays, the notion that Freedom was a greed move on the part of NCSoft was also not supported by the facts. It was NCSoft that, after the Cryptic buyout, radically increased the amount of resources City of Heroes development had to work with. Cryptic was the company responsible for starving CoH, because they needed their resources to fund development for Marvel Universe Online - which eventually fell through. When NCSoft owned the game they pumped a lot more resources into the game without increasing its costs to the players. They continued to sustain that higher level of development for four years before moving to the Freedom model which *still* gave subscribers more content for the same costs. However we view NCSoft today in terms of the shutdown, we can't fairly accuse NCSoft or Paragon Studios of being greedy without some evidence they tried to make more money for less game, and there's no evidence to support that.
When you eliminate the objective basis for greed, reverse subsidization, and unbundling, you're left with only personal preference as the reasonable basis for objecting to Freedom's ala carte content. Which is fine, but, invoking my mandatory Spock quote today, the needs of the many outweigh the needs of the few.