Seems that way... after 22 duplicates i got what i needed, 14 of those 22 are same skill (Worst for my class really..) rest 8 is like 2, 3, 2, 1 between rest.. One with the least duplicates is something that can kinda be considered the best or second best for the class. 0x of the most important as dupli. 14x out of 22 gets statistically really stupidly low % when it should be 16% for all.
regarding that 14 duplicates of the same shitty skill , i have none of it
everything else is duplicated and as an example frosty fire is at 10 duplicates now
i still don't belive its the same rate but you guys might know better probably
The issue is you can't prove it has the same chances to drop for all items.
Anyway, I talked mostly about manastones crit strike and other types - chances are obviously different. About shugo - can't say anything cause i got needed skills from very first boxes. Yday I wasn't succed in selling box, so I opened by my main and got one more needed skill