When you pay to dine at a Michelin starred eatery you do not expect canned tomatoes in the sauce.
If they were used because the skills test only allowed limited time to create the dish, why not provide the chefs with fresh pre-stewed tomatoes? They were given freshly roasted onion. So why not also use pre-stewed, fresh tomato?
I'm a home cook and I make every effort to avoid canned tomatoes because they taste like canned tomatoes.
A cooking competion as high caliber as Masterchef Professionals and a chef with the reputation Marcus Wareing enjoys has no business using canned tomatoes in any way shape or form.
It destroys all credibility.