Look at your math again.
2% from hoj
5% from sword spec
x 3 instant attacks
6%
15%
in the same global cooldown to get another extra attack.
lets say hoj procs in the same global
8%
20%
Sword spec because 1 in 5 is high (how often do you crit with your %?) also in the same global
10%
25%
You math is true until you get a chain proc, then it increases because there are more attacks that multiply the chance