I think Colt is talking about how the classes feel like during different times spreading from expansion release to patch 6.55. The biggest offender would be the gear ilvl. I know WoW is a different game, but there are some factors that are similar. I can state an example with Holy Paladins who are excellent at single target heals with Beacon of Hope copying the full heal to the target during Wrath of the Lich King. So it's kind of like Kardion and Synastry on steroids.

Halls of Lightning final boss

Wrath of the Lich King Expansion release - this encounter features very juicy AoE pulses of lightning damage. Paladins had troubles with raid AoE healing and needed to use a glyph to add splash healing to off-targets. Something like 10% of the original healing. All 5 people had to stack pretty close. The boss also did a deadly nova on occasion that required everyone to get away at least 30 yards / yalms. The pulsing AoEs were still occurring, so everyone moved with the Paladin as they cycle targets with Flash of Light / Holy Light spam.

100 ilvls later with final patch - The Flash of Light and Holy Light casts as well as maximum party HP are now so powerful that the heals pretty much instantly heal 2 targets way beyond the damage of the AoE pulses. Nobody really needs to stack anymore as long as the Paladin continues to change targets with their heal spam.