Heet allows the fuel and water to mix so that a tiny amount of water can be burned with the gas. Heet will not overcome large amounts of water. The label says one once of Heet per gallon.
I would say your mower with 30 hours on it has either older gas, or gas with water in it, and possibly needs a carburetor cleaning as well for it to run 100% right.
Seafoam contains 4 main ingredients, with one of them being the same as Heet. People love taking shortcuts in life, but they often don’t work.
One of the downsides to buying from a big box store is lack of service after the sale. You are just a number to them, and a customer for the local small engine shop.