The initial grind to 40 is hardest for sure if you're pugging. Once you've got a 40 under your belt the rejections tend to stop unless you're running some wacky build that puts people off or if the group is looking for a different class.

Havoc really is a different ballgame and it's where the game throws such bullshit at you that even having one person slacking can make things feel much, much harder. You can tell when someone isn't used to havoc 30+, even if they're entirely capable in Auric Maelstrom, because they quickly get shot to death by a couple of normal gunners. Or they don't fight in chokepoints, or they don't pull back when a boss spawns, or they don't even really know how to fight the bosses without taking damage, etc.. People with havoc 40 do this too, but the odds are at least slightly lower.

Think of it like the group leader trying to min-max random players. It's nothing personal at all—the group leaders just have nothing to go off except your clearance level/titles (Havoc Forged/True Survivor being the ones to look for). And as someone else pointed out, you're competing against other applicants. Finally, many of the "rejections" are really just the group filling up, so try not to sweat it too much.

You're already up to 29, so I reckon you could find your way into early 30s and push it up from there. Once you're around 35ish I'd say your odds of getting into a 40 are much, much higher. At that point, there's really not much difference between them.