All this Mahjong talk makes me sad

Its such an awesome mini game once you get used to it. Then again, it took me like 5 years on and off learning it from playing Yakuza. Once it clicks your set for life! I only worry that one day they'll throw a harder Shogi requirement out there that I can't do. Then again, maybe that'd get me learning Shogi properly like Mahjong...
Anyway, back to your Yakuza 6 point - its dead easy to 100%. Most of the trophies are just for playing stuff and not mastering them, I don't believe there is any Mahjong centric trophy (at least not a hard one if there is) and the completion list trophy is reduced to "clear 100 items in the completion list" and there is way over 100 items on the completion list to finish. Most people will get that trophy just by playing the game to completion (unless you only do the story). Heck, even Amon's requirements are way relaxed - you just have to clear 2 side stories to unlock his boss fight, as opposed to doing all of them this time (though you'd be mad to try taking him on early in the game!)
And finally, you can cheese the Legend trophy on 6 just by keeping a game save at the final boss, reloading it after you finish the game and then up the difficulty. Job done, trophy unlocked! Its by far the easiest plat the series has, and probably the second quickest after the PS3 HD release of Yakuza 1 (well, in theory at least).