I'm not sure what you want to say here but the core difference is, of course, the better critical profile of the Elemental Bloom.
A better critical profile makes such weapons always "win" if your damage bonus is high enough.
But maybe you don't understand the mathematical connection?
So I try to explain and of course, I hope I did no mistakes because to err is human
Critical hits produce at the end basically only additional "free" hits if you are lucky so if you critically hit with a weapon with a multiplier of x3 it is the same as if you would hit 3 times at this moment.
And the critical thread range increases the chance that this happens.
The staff of Shadows 19-20 and x3 produces 23 hits on 20 tries (a miss on a 1, 17 normal hits and 2 critical worth 6 normal hits).
Elemental Bloom 17-20 x3 produces 27 hits on 20 tries (a miss on a 1, 15 normal hits and 4 critical worth 12 normal hits)
the weapon dice and the enhancement bonus together with the other damage bonuses you have, give you the average hit for each weapon.
Staff of Shadows 5[1d6+6] +15 = 47.5 + x
Elemental Bloom 5[1d6] +7 = 24.5 + x
x is the additional damage bonus you need so both weapons do the same damage so the equation is:
23*(47.5 + x) = 27*(24.5 + x)
1092.5+23x=661,5+27x
4x=431
x=107,75
So the result is you need an additional damage bonus of 107,75 and then the Elemental Bloom does the same damage as the Staff of Shadows (if you always hit besides you roll a 1).
So 5[1d6]+115 17-20 x3 is eqal to 5[1d6+6]+123 19-20 x3
Also, this is only a very crude calculation because it doesn't take into account that you have Seeker effects and effects that change your weapon dice like A Dance of Flowers and if your critcal profile is changed from enhancements and EDs it changes too.
And it doesn't take into account grazing hits.
Because of the sheer numbers of factors in DDO, an exact calculation is not that easy.
Of course, an exact calculation is possible maybe even for me but the question is if this is desirable for me.
At least as a player, I don't really want to do that kind of math because it also takes the charm away if I knew the exact numbers.