I have my reservations about Stroll, but i don't think he is that bad. His racing record in f3 and other series is not bad before f1.
His F3 record is the same almost as Hamilton, 5th in first year, winning dominantly second year, but he skipped up to F1 much earlier due to the way things are run nowerdays! (Max for example)
Technically, Stroll did better than Max also, as he actually won the F3 championship for a start. Although Max did better in his first year.
He is not as bad as people make out, hot headed, maybe, entitled, perhaps, but rubbish? I don't think so!
*edit*
@Mr Jack beat me to it!
I'm not sure why you think Stroll is that bad, his record prior to F1 is solid, he's done okay in a mediocre team. In his first season he was the only driver not in a top three car to take a podium. He wouldn't be a candidate for promotion without his dad's money but he's doing as well as can be expected in the car he's driving.