Im not saying it's outclassed by Dragonite's Bulky set because of the difference in the actual bulk.
Basically, your adding HP, and Defense EV's, not worrying about his Sp.Def stat since it wont save him from anything special. With this, you can stop the more physical checks, and especially those with priority from utterly destroying Ono. 76/90/70 aren't bulky in retrospec, but are "average", meaning that it compared to other sweepers who can be alot frailer, he can atleast take a hit better. From there, you look at the other stats, in which you still need a good amount of Atk, and not so much speed (minimum speed EV's can be 80 since your main goal with Ono is to reach that +2 Marker so you can outspeed your problems).
So essentially, your not making a "Bulky" sweeper, but a more reliable one that is not as frail. If your looking for a true bulky sweeper, then there are other pokemon, like Nite, that fit that better because of better defensive stating, and access to some sort of recovery.
But yes Kira, the point is, Ono isn't "bulky", but by investing in bulk, i.e. his HP, and Defense, you make for a much "bulkier" Ono that can take a hit, and still do the same thing that the other sets do (and in some cases better).