Generally Confused and tilted

So I was wanting to practice some cass in draft pick and as i picked my cass the enemy mid lane picked yas. I rolled my eyes and decided to just play careful and wait to engage him till i had some items. So i played the lane fairly safe poking yas when i could until zac started to gank me. The first gank i died due to low health and i was a little out from tower which i perfectly understood. But what proceeded to happen made me very confused and upset. me and yas were about the same level with him being ahead just by 1 level and no item lead. Every 5 minutes or so zac would come in dive me under tower when i have full health and then yas would ult and instantly kill me before i could even touch the ground. This happened over and over and yas would just spam his mastery and type in chat claiming yas is weak and hes in a very bad state. Am i just bad or is this true?