U can buy sippy tops for the avent bottles? Cool. Might have to look for them too. Chloe was having a go at holding her own bottle this morning, it was so funny, when she finally got it in her mouth she would keep putting it so far back that it made her gag. But she got the hang of it (ish), I will try post a vid of it sometime! 
KA, I wouldn't stress about it. As someone else mentioned, even Dr's have differing opinions on a lot of things, and Ethan is thriving so I don't think you have anything to worry about. He certainly doesn't look like you have deprived him of a thing 