Part of the problem here was your teamcomp: you as Sivir was the only one with any meaningful amount of ranged poke, and three of your teammates were pretty much locked into melee fights against a team who loves to brawl it out in melee. You had two dash-based champions into Poppy and your entire team was squishy allowing AP Cho and Crit Garen to wipe the floor with your face. You also rushed LDR against a team that built almost entirely squishy, actively removing yourself from relevance. A quick press of tab would have showed you that they were building full squish and you should go about your normal build.
Your team also fucked up pretty badly. There is no reason why Yasuo should have lost lane to Cho'Gath, a champion with highly telegraphed attacks and horrendous mana issues. Yasuo has a strong early game and should have abused that mercilessly to kick poor Cho around and stall out his ROA powerspike. Somehow your Janna/Sivir botlane, which is basically kiting incarnate, lost to an Alistar/Garen lane, a lane that has zero poke and shouldn't, by all rights, have had any kill pressure on you with a Janna watching your back.
tl;dr: they won primarily because of a series of mistakes on ya'lls part and a somewhat favorable overall team composition, not because "tank" comps are "freelo"