In the case of, say, support of a new(ish) colony, or in "relief operations," this is probably the most practical approach, I agree.It is a foregone conclusion, especially one based on the Ariel drawings, that a small-craft carrier ship is going to be larger and less maneuverable than cruisers and such.
Given this, I wonder if perhaps the Federation would employ a completely different kind of "carrier" strategy, by not using a dedicated "carrier" starship at all. Look at it this way: a transport-tug class of starship (like FJ's Ptolemy, or, better yet, Forbin's Sultana concept) could haul multiple cargo pods. Maybe there's a special kind of cargo pod that serves as a "carrier", so that each pod is a self-contained hangar, launch system, and crew module containing everything needed to support the launching, maintenance and recovery of small craft. The benefit to such a tug-based "carrier pod" system is that a tug could haul multiple pods to a destination, dump them off, and each pod could act as a temporary space station until the tug would come back to pick them up. If we assume a Sultana-type tug could haul at least four "carrier pods" to a "base camp" point, I would expect that it would be far more than an Ariel-type ship could bring to the scene. And the tug could leave the pods there and go on to other assignments, meaning that launch operations in a given star system would not require tying up a warp-driven starship indefinitely.
The pod needs minimal, if any, weapons system. It requires only basic low-output power generation system. There would be no need for FTL propulsion, or any of the other systems that a starship requires.
You can look at this as being the equivalent of, say, the "trailer cities" which were deployed in real life in New Orleans... temporary "permanent" facilities, basically.
And you're absolutely right, you'd need quite a few of these. The sense of SCALE seems to be something that poeple miss on occasion. A single Galaxy could wipe out a city with barely any effort, but to support a city, a Galaxy simply is too small... not enough people, not enough volume, not enough capability in general. You'd need a HUNDRED "Galaxy class" ships to support a major disaster in NYC, most likely.
It's much more effective to have a hundred dedicated (and LOW COST) "relief pods" which can be deployed to a site when needed. You could probably deploy those resources for the cost of, say, just two Galaxy class ships. And these resources would be better-suited for the job anyway, since so much of the Galaxy's resources are focused on exploration and analysis.
For that matter, for evacuation, you'd want dedicated craft (or "pods" perhaps) for that purpose as well... again, the FJ "pod" concept is really well-suited for this role, as you correctly point out. The so-called "liner pod" he came up with would be orders of magnitude less expensive than a full starship, and could be loaded up, left in a "safe spot," and cycled through repeatedly, without the need to carry everyone away to the final "offloading" destination at once, or even to KNOW a "final destination.
While I never really loved the Ptolemy-class design, the transport pod design was a great idea, wasn't it? My preferred "transport pod carrier" concept was the one based upon the Grissom's general design, really...

Imagine a fleet of these "wrangling" a much larger fleet of these...
(both of the above taken from this website)
http://www.modular-models.com