Unless the consumer have subpar hardware to begin with, not everything is programmed for the lowest common denominator, nor should they be. That said, I do agree with your other points.
can't say I've seen this happen personally, I've rarely seen anyone suffering frequent DC in the dungeons, and the few times it happened it was due to ISP problems on the player's side.
On the issues of client and hardware, it's obvious that the client optimization is hardly up to par, but at the same time I think some are placing a bit too much of the blame on the client. There are way too many things that can cause the issues that people have talked about, and not many have provided enough information to really figure out what the problem may be, and I suspect not many have done all that much testing themselves either.
hardware, software and OS configurations and settings, parts selection, cooling system configuration and condition, ambient temperature etc. can all have substantial impact on your system's performance.
I personally haven't really run into much issue with the client myself, and I'm running on a decent, but hardly top of the line system (i7 920 @ 4.0ghz w/ 6gb ram, a 580gtx and a couple SSDs for the OS and games). I run the ff14 client @ 1920x1200, with mostly standard (because higher settings don't really provide any noticable improvements anyway) settings and 4x AA, and for the most part the game stays within 45-60 FPS for me. Hell, sometimes I even run ff14 with multiple instances of eve online clients at the same time with no issue. (all in windowed mode).
can't really say much about a direct comparison between HDD and SSD performance for the game, as I've always had SSDs in this system, but I never experienced any stutter or other notable performance issue with the client on my laptop, which has much less power being a c2d p9500 w/ 4gb and only a 4850m gpu, and no SSD - I just had to run the client in a lower resolution in accordance with the less capable hardware. As far as I can see, the SSDs loads the game and zones a bit faster - when I teleport both clients at the same time, it can take a second or two longer to load on the laptop, but otherwise I see little differences between the two.