To call Yi an Assassin is...weird. He's DPS based, not Burst Based; even in a full blown Yolo Crit build his massive damage is backloaded in hitting a lot of times over a given period. Yes his tag is that he's an Assassin but to be frank, the label doesn't describe the product very well in this case. Hell, ask most people what they think Yi is and they will tell you Fighter/Melee Carry/Light Fighter first the vast majority of the time.
Also, building BorK on an Assassin is also really, really weird once you think about it. Makes perfect sense for a Fighter (like Yi), but Assassins in general? Odd choice.
Now back on the topic at hand; Yi is a Fighter to be frank. Both Rageblade and BotRK are perfectly acceptable as Master Yi items (in fact Cowsep, who I personally regard as one of the best Yi players in the world, made a video on the subject). Your friend, I'll be frank, is kind of an idiot for thinking one of the items with the greatest synergy with Yi out of the entire item pool is bad on Yi.
Now, the entire point of Fighter itemization is to build based on the situation. If you watch the video, Cowsep directly compares Rageblade to BotRK and explains the whens and whys to both items. Now think about that sort of comparison for most every other item in the game. Yi has a lot of multiplicative power when ahead which is why he's such a dangerous threat when going full damage Yolo build while he's fed. A Yi that team fights must have an answer to enemy Burst, and because Burst is usually Magic Damage based, items like Spirit Visage or Maw are obvious candidates for allowing him not to explode upon entering a big fight. Titanic Hydra is a good way to remain a damage threat while you're tech'ing enough Health to survive enemy Burst, and is a definitional Fighter item after the Juggernaut rework and Fighter items becoming more Health based.
Think like a Fighter. Be flexible to the environment and build around it. Build a bad habit and insist on sticking to it above all else, especially a habit that's straight up inaccurate like treating a Fighter as an Assassin, and you will be left behind.
its essential on yi, i have played a lot of 
recently". I said "OK, right after finish my 
(i already had 
)". To my surprise he responded "No, don't build BORK on Yi, its bad."
and other tank items. I thought he was trolling me. Surely the current meta couldn't be tank yi.
QQ Riot buff pls
