Raid-level content is another thing entirely though; you can technically start it at level 50 with Extreme Primals and the Binding Coil of Bahamut
Vet Questions:How is the raiding and dungeons Final Fantasy XIV
The 4-man dungeons are meant to be "light" content, so they're not too tough generally. Veterans shouldn't have much difficulty with them unless you're getting other really... questionable skill players. Mind you, you're still at level 25, which is easy in the realm of intro dungeons; the first content that even starts to challenge most players isn't until 32+ as the game starts adding more complicated or punishing mechanics. Essentially, the game is just trying at this point to drill into you the basics (Don't stand in bad. Attack adds. Etc.). Ifrit was essentially a basic competency check.
Raid-level content is another thing entirely though; you can technically start it at level 50 with Extreme Primals and the Binding Coil of Bahamut; and there'll be even more once you hit 60. Now, some of that 'high tier' content is more difficult than others for a variety of reasons, but there's adjustable challenge options now too (Ifrit Extreme in whatever level 50 gear you want is a massive difference from an undersized party or minimum gear level fight with Ifrit EX). I'm sure there's plenty to challenge players who're here specifically looking for it.
In terms of damage, generally speaking.Melee DPS > Casters > Ranged Physical. The big catch here though is that these actually level out in general due to things like having to handle mechanics, the need for spacing in high level content (You really can't 8 melee range a lot of fights, it just Won't Work for various reasons), etc; so there's generally a call for every class.
Well, depends on if you want to qualify Ravana Extreme or not (It certainly has the difficulty one would expect). And by the time the OP would get anywhere close to 60, Alexander should be open and running.