There is already ranked content in this game that is swayed by RNG. Triple Triad tournaments, Mahjong, and many other in-game competitions are examples of things that are affected by RNG but are also highly skill-dependent. In Triple Triad tournaments, you are limited to 20 games per tournament and can thus be hit hard under some of the rule sets by RNG; I've come in 1st place in some tournaments and not even made it into the top 6 in others because of this. With respect to Ishgard rankings, if the detrimental conditions proposed above always followed a beneficial condition, I think that it would actually allow players to plan ahead better (you could obviously observe through the detrimental conditions, but this would incentivize using other non-touch/synthesis abilities so that you're not burning too much CP on just observe). I understand that limiting the number of crafts would increase the impact of RNG as 100 may not be a large enough sample size to dilute its effects, but the current way of minimizing the impact is just to craft an absolutely ridiculous number of crafts, which gets back into the issue of "more time = higher rank" (which I consider to be a bigger issue). As I mentioned previously, during this ranking season I achieved the highest score on any class on my server (Gilgamesh), but it took a ridiculous amount of time to do that during the 10-day period; it was enough hours to be a full-time job for a lot of folks, and it continued throughout the weekend. I think the Ishgard rankings would be a lot more accessible to people if they had a finite number of materials to work with. Speaking which, to address another point you touched on, you would just be given a set number of materials (e.g., 100) at the outset. It would be like beast tribes or other collectible turn-ins so that you could craft it on whatever class you want, but once you used them up, that would be it. This way you couldn't just switch over to another class and get more materials. If someone wanted to try and get the achievement on an alt that was fully geared out, then sure, why not. If each craft took about 10 minutes, that would be another 17 hours they would have to spend on their alt trying to craft all of the items.

At the end of the day, I think that someone who really plans out the crafts and tests this out with trial synthesis beforehand would be able to achieve a better overall score than most other folks over 100 crafts despite any unfavorable RNG they may run into on some of their crafts.