I agree regards his lack of career goals and like you I have concerns about his record elsewhere.
But at Tynecastle he worked his socks off, rattled every single Hearts defender, put in some thumping tackles, layed the ball off well, played countless one twos with colleagues. Still has areas to improve but a massive improvement from previous games and a performance that earned him a standing ovation when he was subbed. His team won the game and he contributed.
Maybe he won't score a ton of goals or maybe he will. Time will tell. But as long as he contributes as he did on Sunday and helps the team to win, then nobody will care if the goals come from others. On Sunday's performance he deserves his chance.