Apologies also.
I often do consider language issues, but your English was good enough for me not to even consider that it isn't your first language.
I understand what I write,but that is no guarantee that others will, I cross my fingers.
The situation here, of unwelcome outcomes, is the same kind as discussed in the upgrades of gear, and ages ago when they introduced the special gems and the complaints of not getting them came in.
With respect to your 'I should eventually throw all 6 numbers on a die,and if I keep on hitting a ghost the probability of success will increase.'
With the die, more likely.
With an attack, the chance of a particular item is fixed for each attack,and doesn't change the more times you attack, the likelyhood of not getting a favourable outcome is a different, but connected, mathematical concept.
Consider these .
If you have ever played a board game,eg Ludo, that requires a 6 to start, you have probably been in the situation, where an opponent is half way round possibly with more than 1 token, before you have even started, and it's the same die.
The advantage with a die is that you can see there are only six options each with the same theoretical chance of showing on the top face.
Considering attacks on, ghosts/invaders, you effectively do not know how many of each item is possible,they do not say this, and so it also gives them the ability to change it.
Also, if they said in order to get enough rune fragments to complete one legendary item the spend would be millions of energy, and the bonus given was really infintessimly small, many would think twice about even making the attempt, so they don't say this, just let you think what you want, and go ahead chasing, and spending, which is the desired goal.
Like the stores do not tell you that the free item,in the 'buy 1 get 1 free offer' is something you don't really need and could perish before its used.
Supposing all your socks where black except two white ones , and you could only take one at a time out, eventually you would make the white pair, but it would much more dificult if evey time you made a mistake you had to put the black one back , it would take much more time, this is effectively what happens when an attack happens. Each attack is a separate attack with exactly the same variety of events, there is no real connectivity that leads to the desired outcome.
I looked at the link you sent.
I often find that website unhelpful.
What exactly does Often mean?
How up to date is the information?
I would expect that the more useful items are less likely to drop, and it can take a long time to get desired items, such that by the time they are obtained, they are somewhat redundant as the bonuses are then not so significant.