I do think fellaini is a fairly poor comparison - I actually do remember him being pretty bad in the first few appearances but he did always have that tactical reason to get included in a team - his size and ability to bring balls down from the air or flick it on, defend and attack on set pieces etc.
I really struggle to see what tactical advantage (size, pace, engine, aerial ability) that Sandro offers at this moment in time which makes a very strong case for him being included in the starting XI to counter his shortcomings so it seems so unlikely that he will get time in the 1st team to play his way into some form. he just doesn't seem strong enough at any one thing to make a case for playing him and dealing with the time required to get him up to speed
First few appearances mean fuck all, being 21 and coming from Belgium to the Prem is a big step up, I gave him time to adjust before I judged him. He was wasted up front, but he still used the natural attributes to be one of our main contributors that season. For that reason, I can't call him poor.
Totally agree with the Sandro point though. For the style we're starting to play, DCL is much more suited to it. I do think Sandro could be a player, but it's the wrong time for him.