It absolutely produces different outcomes than a two party system. Smaller parties make demands as a condition for joining any coalition (or similar arrangement). For example, Canada's NDP only agreed to back the Liberal Government on condition of state funded dental care for children being implemented. Now it is. Millions are affected. Whether you agree with it or not - that is unquestionably a "meaningfully different outcome". Other examples abound if you care to look.
>I'm not aware of any parliamentary system with a wonderful diversity of thought and a long record of positive accomplishments.
That's an impossibly high bar. The standard we're talking about is whether it's better than a two party system.