OK really, why the fuck can you stack items?

I seriously don't understand why its possible to stack certain items. I essentially lost my last match due to the fact that one player managed to get and stack two Guinsoo's on their Vayne and melt my team like crazy. Another player, or presumably the same one, got the same on their lvl 3 Fiora along with a Zepher and it was basically impossible to kill them since they would attack so fast that they would get their ult back up, stun, and hit me repeated, rinse and repeat until I kept losing. I COULD DO NOTHING!!!

HOW??!?!?!? How the fuck is this game mode fun? If it's not bad enough that I repeatedly fucked over by the RNG for lvling my champs and needing the items to build, the fact that you can just stack certain items on some champs to have them become unbeatable monsters further cements my hatred for this mode. I've tried. I've fucking tried to like this mode but it's just utter shit to me!!!!!!

All of this just makes me want Legends of Runeterra to come back up, because at least in that I can get the comp/build I want, I can play how I want, I can have more control over the situation if I have the tools. This mode is just "build a team, get screwed over by RNG while your opponents get favored by it and stomp you."