Devs always say crap like that.
The problem is players want mutually exclusive things, so devs tend to tell them whatever they want to hear even when it's contradictory. Like players want a massive game world, but they want instant travel everywhere. They want to advance their character easily with no limits, but good lord in heaven no one better be able to advance faster than they do.
So devs always say progress is horizontal, but at the same time actual in-game stuff gives vertical progression. They'll probably balance it similar to AO, where gear increases in ability linearly, but exponentially in cost.
So someone in 10k value T4 gear is at strength 10, and someone in 10M value T8 gear is at strength 13. In a full loot game this actually is balancing, because it means a skilled T4 group has a chance of winning big but only losing small.