I think he was / is incompetent, unfortunately. Not incompetent across-the-board; he managed many aspects of his mayoral role fairly well.
But in those two cases, SSE and SmartTrack, he would have to either devote a fair amount of his own time, go into all details, and get it right. Or, find a reliable technical expert who can do that for him. And he didn't do either.
Cost was certainly a factor, but not an excuse. He didn't have to assemble all funding from scratch. He had the city's SSE surtax voted for before he took the office, as well as substantial provincial and federal funding commitments. Still not enough? He could alter the scope of SmartTrack, he could look at partly surface / elevated options for SSE. Potentially, he could try combining SmartTrack with DRL (using mainline rail for DRL), and he could evaluate the so-called SmartSpur (SmartTrack with a branch straight to STC).
Perhaps one could have tried all of the above and still not succeed, but he certainly didn't explore all options.