not just one, both of them, normal urf is fun for about the first day or two then it devolves into 5 man premades with shitty anti-fun push comps, sure you can pick a broken champ and get some kills, have a bit of fun. but i hope you have fun losing anyway because the enemy team has an obnoxious comp based around pushing towers.
as for arurf? it would be fun, if it was actually random and we had bans, there are too many auto lose champions you might aswell let it remake if you see them in loading screen, wow your team has yasuo and maybe a few adcs? cool the enemy team has a morg and a yi have fun with a gray screen most of the game wishing you never queued up in the first place. not only is there that coinflip theres also the fact yi and maokai are gonna be in 90% of your games but trust me you wont see a single xin zhao or leona because they basically dont exist in the mode because we all know pretty much its only kinda random, not fully
and the more i think about the first example on urf the more i realize most temporary modes are exactly like that, its fun for 2 days till people find abuse-able champions or strats that flat out ruin the mode for anyone else not doing the same thing and just wanting to have fun get driven out of the mode completely