Where should I practice?

So basically I just finished my provisionals for the first time and I got ranked Gold IV. But as it is the preseason and a lot has changed, I'm still testing out champions to find ones that I like (I only played familiar champions in ranked). So I got Twisted Fate and I really like him but he is very specific in who he's good against. However, I still decided to pick him in daft pick just to practice, and they picked fizz AFTER I had picked TF...so they countered me. So I played the best I could, but still just couldn't do much even when using ult into lanes. It didn't bother me until my jg, Kayle, started saying "we could have won if mid and top didn't feed. My team sucks". I just told him/her I was just practicing and they happened to counter me, I didn't mean to feed. This person told me I shouldn't waste everyone else's time. So my main question is should I just practice in blind pick? Was this person right that I was wasting their time by playing fairly new champions in daft pick(I played a few bot matches and had already won a few daft pick as TF but I'm still getting used to him)? If he/she was wrong, then should I just ignore these people because even if we had a chance, having a terrible attitude isn't going to help.