Would you improve if the content required it?

[Naunet]

People tend to want their victories earned through their own merits and skill rather than coming out on top just because they got lucky that the boss did not use a tankbuster move 3 times in a row.

While I agree with this in part, I also think there are ways to design fights that incorporate the learning of challenging mechanics (and the sense of accomplishment that comes with being able to do so) while also avoiding the feel of this perfectly scripted dance.

Phageborn Convergence in WildStar's first raid Genetic Archives is a great example. There are five bosses, and on any given week one is not active while you fight the other four. Each boss has core mechanics that you need to deal with in different ways, so there's some strategic planning involved when you first get to the fight, but periodically throughout the fight, one of the bosses becomes empowered and teleports to the middle. When this happens, everyone must turn their attention to dealing with a new mechanic that is unique to that particular boss's middle phase. There is no pattern to which boss teleports to the middle, which forces the raid to adapt depending on which one is up at the time. Some of the middle phases require a large degree of coordination with the raid, such as "hammer" middle phase (the boss wields a giant hammer, hence the nickname for him lol), where he gains 20 interrupt armor and starts casting a very large absorb shield. Every time someone hits him with an interrupt, it does massive raid-wide damage, so the general strategy is to coordinate 5 groups of 2 people interrupting in turns while being mindful of the raid's HP as the healers recover from each raid-wide explosion. Once you've interrupted him, the middle phase ends and the raid can split back up to wherever their previous assignments were on the different bosses.

That's just one example, but I think it works well in blending practiced coordination (which I don't think should be undervalued, especially if the coordination is challenging enough) with a certain amount of unpredictability.

[edit] "Randomness" can also occur in how a mechanic is applied to lend variety, such as the distribution of big and small bombs in the X-89 fight, the first full boss in GA. If you're chosen for small bomb, you have to run and drop it at the edge of the area (when it explodes, it destroys one of the hexagonal platforms the encounter is carried out on), and if you get big bomb, you run off the entire arena to avoid destroying the entire platform (when the bomb explodes, it will bounce you back up and you can aim for safety as you land). They are mechanically rather simple, but you never know if you're going to be the one given a bomb and which one it will be, so you have to pay very close attention to what's happening to you - and what's happening around you, in case another raider misses that they got the small bomb, so that you can get away from them before it explodes and destroys the hexagon you're standing on.