How many people here have managed to reach tier 4 in 5e after starting from tier 1? I have heard that it is a hard thing to do.
Well I suppose it depends on the pacing of each game, really. But I've done some math with XP in various editions, and 5e seems to be the edition that hands out more XP thus far. So in theory it should be the faster one to level up in.
5e:
A CR 15 monster gives 43% of the XP a level 15 character needs to level up.
A CR 10 monster gives 20% of the XP needed.
3e:
A CR 15 monster gives 30% of the XP a level 15 character needs to level up.
A CR 10 monster gives 5% of the XP needed.
2e and earlier:
Here it's trickier to compare because there was no notion of CR in 2e and earlier editions, Hit Dice being the closest you could use to compare but even then not really very appropriate. But rest assured that leveling in 2e was MUCH slower than any more recent edition. Probably because 2e considered 1-10 (~ish) the level range for "normal" adventures, and beyond that it was more or less "epic adventures" already. Even a famous epic and powerful character like Drizzt was level 13 or 15 in 2e (depending on the timeline of his career). Getting anywhere near level 20 by standard 2e XP rules would require a loooooooong years-long campaign of frequent game sessions. Most people cheesed it a bit by rewarding lots of XP for completed adventures and such when playing beyond level 10.
------
Edit: Also, 5e has a LOT more healing/recovery than 3e or 2e, so in theory you can face more encounters than before at a lower risk. Thus allowing for a quicker progression pace I imagine.
I know 4e also had lots of healing, but I haven't played that one, really, so I can't speak for it.