Hm... reading that response, I realize that I am trying to avoid the specifics in a conversation with someone who explicitly needs them, and wasting your time as a result, so instead:
I have PRI Blue Grade Awakening weapon. With only 3 previous fails (from ANY attempt on ANYTHING) upgrade odds are 10%. Chance of downgrade, nil. I can use items that I can farm about 10 per hour of while ALSO making money otherwise, and try to upgrade this as many times as I want if I can repair it (which is actually not super easy but only if I am being REALLY efficient, I can burn money to do it).
Failing that about... 5-6 times will get me to +16 or so Failstack. My odds of upgrade then are 20%. So if I wanted to upgraded this to "DUO" it'll take me... somewhere between 5 minutes and probably 3 hours, and somewhere between 0 cost and I guess 'the amount I would farm in 45-80 minutes.
Then I have a DUO 'Yellow/Gold Offhand' from a Boss. If I START from that +16 I have a 17% chance of success and otherwise it will go back to PRI and cost me a bit more than the above to DUO again. Maybe... 2x as much (efficiency barely matters for Yellow grade, there's only really one option.
Every time I fail it, I'd have to do some shinanigans to get it back to DUO, but the Failstack goes up and raises the chances. Meanwhile, I could basically still use it so I might not even care. If I fail it enough times, I'll get to a point where I go 'you know what, I'm just gonna save this and bet on some lower numbers.
At some point it will go back to DUO, but I might have built up a 40 or 50 failstack while trying it, which I have in reserve for TRI-ing it.
Here's a chart.
So about 30% chance, and I'm just throwing the money at it, and throwing it more, and it's multiplying.
L2 is the same. You throw the money at it, you get the crystals back. BDO you throw the money, you get the failstack and you get to keep the gear.
IF people in BDO really hate 'the throwing of the money', then they will hate it in L2 also, is my reasoning. Each upgrade is a jump of about 9 Attack for the Blue Awakening weapon I mentioned. (which seems like a lot, and it sorta is, but in PRACTICE doesn't change too much until you have a lot of different things in tandem, for reference I recently attempted to PEN my TET mainhand, dropped it to TRI, and I have not cared or noticed since).
The thing I counted in my calculation was simple.
In BDO you try something at a 33% chance, and retry it at a 33% chance, and if you fail both times you end up with a weaker weapon that you can retry a lot with.
In L2 you try something at a 66% chance, and keep going until you fail, and IF you fail, you now have no weapon.
I'll spare you the statistical distrubution graphs. A BDO player's chance of 'going straight from PRI to TET' assuming that they have built enough stacks to have 33% odds DUO and TRI and a measly 11% on the TET attempt, is basically 1%. So if you were the sort of person who just 'never prevented level loss' you'd be 'taking this 1% chance repeatedly' to get your gear to the second highest it could possibly be, but at 11% chance to get to 'reasonable'.
General quickwork indicates that for L2 this 'reasonable', where you had your 11% chance starting from the bottom (yes, this is explicitly NOT doing the same as the BDO start point), is at +8. 5 Successful enchants in a row.
Average loss of items in the process if you start from unenchanted singles every time is by 'definition' 10 items and about 30 'enhancement items'. And just like BDO, you could 'start with that and end up with no progress'
Well, that's about enough, right?