I don't know if it's the same for everyone, but isn't the drop rate of Aki's (Akiza) skills painfully low? I've got her to level 35 and the only drop skills I obtained was Draw Sense: Low-Level and the god-awful LP Boost Gamma, while when I switch to Ryuzaki (Rex), it only took me 7 duels to get 3 of his skills.
Yeah it really is all about luck. It used to take me a month to gather all of the skills of a character while I played rank duels (trying to get 5 wins daily for the rewards).
When I was dueling Spunky Judai he dropped 3 to 4 of Bastion's skills when I was farming him and just recently in the Yubel event while also farming I managed to get 2 of his skills in one drop.
Like the skill drop as a reward tends to be pretty low when going against LDs but even in ranked you'd have to either play (not necessarily win as I managed to get one skill when I lost a duel) a lot just for a skill drop.
I maxed out my Akiza's skills getting all her skills through ranked. Again ranked is optional but know that it might take a while to get them all.
It's all about luck, my friend.
It took me only several duels against LDs (not PVP) to have Akiza got 5 skills, including What grows in graveyard.