"If you think everyone will go with one build with fully adjustable stats then your aguement is generally invalid in the first place. If everyone will use a same build, they will do that in any system." I don't understand this. The point people are making is that if given full allocation of stats, eventually people will settle on an optimum build. Yes, people will experiment but eventually a few builds will come out that will work the best. Since the game is being geared towards a party system in which people are being encouraged to play roles, a full stat system gives the illusion of freedom. If someone wants to be a battle whm then they're going to have a hard time finding a party to accept them and SE can't possibly balance the system to allow for all builds of any class/job. Therefore, a select group of builds will come out that will be party favorable.
Personally, I'd rather have a system that focuses on roles and encourages people to get good at their roles in a party. Also with the lack of people playing at the moment and with too many choices in stats, then it'll be even harder to make a viable party (can you image having to ask a whm/conj everytime you make a party whether he's an actual healing conj/whm? except now having to do this for every class and job)
Another point is if stats on gears are favored over stat allocation, then this makes gears much more important. This makes crafters a much more important part of the game. I want crafters to have a role. If equipment is negligible then so will crafting and dungeon/boss crawling to get new equipment.
Merit system will add some variety but not enough to break a class/job. It's a nice compromise. To have a full stat allocation, you're possibly throwing away a balanced party system, making crafters less relevant, and making questing less worthwhile. This doesn't seem worthwhile just to allow some experimentation with a kitschy class build.