Well the "breaking GCD" problem is not DIYCE issue, actually it's a bit harder to break GCD with DIYCE than manually, as addon "fires" skills about 20% slower (in my case) then theoretical maximum. Besides it's only PvP problem, as after using 2-5 skills in 1 sec, then you will have not 1s GCD, but 2-5s GCD. Of course it is frustrating if you get more than 1 (or I should say due to no GCD skills 3) skills in sec, but this is game not DIYCE issue.
DPS with DIYCE - form my perspective you can gain really much with complicated rotation or many non-GCD skills, so as said before WD/X and X/WD with CC. DK if it would be possible to spam all skills manually from keyboard so fast. Probably it would be - maybe even faster, well DIYCE gave me like 10% more DPS (with good skill rotation) compared to only spamming CC, so supposedly I could beat that easily even with some mistakes, that every normal human makes, not mentioning ordinary in-game macro, to spam CC and 1-2 other skills. So definitely not rouge problem, rather warden. The reason people use DIYCE is they like play simple.
So whats fan from this simple game you ask? First of all for some fun from game is not actually playing it, but checking what's better, improving something, finding some in-game formulas, even being here at forum etc. Second this is MMO not game of skill, so whoever hits the button first win or you have to do that in exact 0,2s or you die (not mentioning that this is current trend in MMOs, maybe that's way some stick to ROM with DIYCE, just to run away from that) - it's more about playing with community, finding dungeons tactics.... Simply hitting 10 keys doing exact same thing (ex. doing DMG) is much more boring, than hitting one for that and for some it could be even one key for DMG and also for healing, immune, interrupt boss spells and whatever you can do with DIYCE. Of course some would like to hit those 10 keys, look for boss debuffs, hp (both self and boss), positioning of everyone else in raid, aggro, tactical phase of boss, energy pool and many other things and this is fun for them (no irony - really). If everyone would like same things there wouldn't be so many games, just one universal super entertaining for anybody.
I would agree, that players just copy/pasting can be an issue, but look my previous paragraph. Fun is not same thing for everyone - deal with it. And form my perspective I know many people simply copy/pasting that do really bad DPS, because they have found some old combo, some would abandon addon, some will keep doing poor DPS and some will learn something to improve their rotation. I have myself start form copy/paste, well I have never really used original pasted script version (as for - well everything I have my own opinion, I also need my own rotation), but it gave me perspective how DIYCE works (without it my knowledge would simply be insufficient), actually I would like every (well most) class combinations included in DIYCE with some not optimized combo, just to give people something to start from. Some will take a shortcut, find some well written script and copy/paste, but they will never be good enough, as probably any change in skills will destroy their DPS, besides they will loose opportunity to make scripts that actually suits them, instead of trying be suitable for the script.
For the things that DIYCE can do.... Well you can do same things and much more with different "tools", so again you can't blame DIYCE, as originally it is not implemented there.