What you state on your original post is precisely one of the main reasons the RDF should never be included in Wrath (except maybe for a small use case I explain below).
The random Dungeon Finder is just a band-aid to cheaply fix the horrible population management that Blizzard does on their servers after some time has passed after release. Right now on a healthy server, it’s just a matter of minutes to get a group for ANY max level dungeon you want (if you are proactively pursuing it, of course; just staying passive on Shattrat waiting for an invite DOES NOT COUNT as trying to group for a dungeon, most often than not it’s way faster you start building your own group)
Yes, people on half-dead servers would benefit from the RDF by being able to group for dungeons, but this is just the tip of the iceberg. A symptom of a much much deeper issue, that the RDF is just trying to hide under the rug, while giving Blizzard the excuse to do nothing about the root cause. But even with the RDF, the problem is still there. A half-dead server is still a half-dead server. That means no group questing, no raiding, no viable professions economy, no viable Auction House, no WPvP…
What all those irate people yelling to Blizzard for the RDF should be doing instead is demanding PROPER server population management after launch. Free server transfers. Server merges (as frequent as needed), and so on…
To ensure that any and all servers stay on healthy population ratios, so it’s easy to group for dungeons, as well as easy to find Raiding parties, good Auction House stocking and prices, etc…
The only reasonable Use Case for a RDF would be grouping for dungeons of lower level content, for alt leveling or late comers, where it’s indeed a bit harder to get groups even on populated servers.