This can't/won't work because of scale. The levels are designed to use those skills that are available at that level, some which have DoT's or other effects. What should be happening is that the ilevel-sync needs to be capped so that someone in i310 gear can't blow away someone in ilevel 20 gear. In i310 gear you can rip hate off the tank if you use cure before they hit 30% hp, where as when you play this as a new Conjurer cure will barely do more than 20%. If you play a tank in any of the pre-30 dungeons, the DPS and Healer will rip hate from you if you're not in equal gear (partially fixed in the current patch.) It's much harder to play a tank if your gear is below the parties gear, because the party will generate more hate than you can.
As a recent example, as the Off-tank in a Praetorium run, In Sword Oath I was #2 for the boss (in i255 gear,) but I was also within 95% of ripping the hate from the MT who was also Paladin in Shield Oath in i120 gear. I didn't want to rip hate completely from them, so I cut the combos in half when it got that close, (because spinning the boss is annoying.)
The more or less way to make it less boring is to make all skills you'd use in a combo normally but instead of "do nothing", fallback to a similar skill. That way you're not having to change your play style just for these dungeons. Your 'bar' would just show aliased skills as available, but if you look at the tool tip it will say "Alias of (skill) until level X"
eg Fast blade, Riot Blade and Shield Lob are the only skills you have normally in a level 16 dungeon for Gladiator/Paladin. If you hit Rage of Halone, do the animation for Rage of Halone, but do Riot Blade. On a Conjurer/White Mage, if you hit Cure II, do Cure I if Cure II is not available. It may be a little confusing, but if you normally leveled on these dungeons, those skills would not even be on your bar. Only PotD is making them available before you earned them.
If you make everything available, you would quite literately have to re-tool every dungeon so that the trash mobs hit harder and have much much more HP to take into account the AOE skills everyone has.