I’m with you on the bad effect of deadlines! But I feel sad that you seem to have witnessed an abused form of Scrum in your company (sadly not uncommon at all). Setting deadlines and controlling feature scope is part of the role of the development team, NOT the product owner. The team is responsible to stand up for quality, which then results in a sustainable (ie health and quality-conscious) pace. Also hiring more people is not done bei POs, but by management (who are top Scrum Masters by definition) or by the team itself (in a fully agile organization).
However, the situation you describe is so common, that people confuse it with agility :(. In my experience the old hierarchies and the unwillingness to really become agile (as opposed to just doing cargo cult Scrum/SAFe/Kanban/…) especially in top and middle management are the big problem. You can only avoid this with either managers who really adopt an agile mindset or with good coaches who teach your company more than what can be read in books about process.