Fail Forward doesn't mean you always succeed. Its basically a recommendation that for checks where a total failure of a check would be anti-climactic or dramatically inappropriate given the situation, the GM is encouraged to change the results of a check from a binary pass or fail, to a pass without complication vs. pass with complications. So the roll itself is still meaningful to the player and the game. While the actual check may not kill you, the complication introduced by it certainly could.
So far example, in the Fail Forward model, lets say Luke Skywalker failed his roll to swing across the cavern with the princess. Instead of falling to his death and pretty much derailing the whole adventure, the GM still rules he makes it across, but suddenly more storm troopers spill out of a side passage, or he drops his blaster on the way across. Something like that.
13th Age is all about cool story, and drama. If you are a diehard simulationist who believes PCs should literally live or die by random rolls of the dice, then 13th Age is not for you. DCC is probably more your style.
The Escalation Die similarly promotes drama and cinematic combat. Starting in round 2, every PC gains a cumulative plus one to hit, up to plus 6 in round 7, if the combat lasts that long. This bonus is represented by the die the DM keeps in the middle of the table for all the players to see. Some monster abilities and attacks also key off the die. The idea isn't that armor becomes worthless as a combat goes. The idea is that as the fight goes on, the PC's begin to see fatigue, weaknesses, and openings in their opponents that they can exploit. It also encourages PCs to save their bigger attacks and spells for later in the combat when its more dramatically appropriate to use them. As opposed to going nova in round 1 and then grinding out the rest of the fight with lesser attacks as frequently happens in D&D.
Personally, I love 13th Age. Its a freaking amazing game. For me, it feels like all the best of 1e, 3e, and 4e. But if you like rules as physics, and things like 4e nixing the double counting of diagonal squares (13th Age is gridless, but its very gamist in its combat rules), or monsters built differently than PCs gets your dander up, then 13th Age is probably not for you. You should stick with [notranslate]Pathfinder[/notranslate] for that kind of game.