We've seen the hulk way above class 100 showings, im sure that others have showings high above that also(probably anyone who's ever held up a building) in your opinion is It a good way to rank strength? In other words why not class 500, class 1000?
I think using the numbers as tonnage is incorrect. To me, Class 100 doesn't mean 100 tons. Class 100 means one of the top classes - able to lift a tremendous amount of weight. When we see Thor lift a mountain, it's obvious he's lifting substantially more than 100 tons. Only Class Incalculable is higher and is reserved for beings whose strength cannot truly be measured. Because of his variable strength, the Hulk is in this class. How do you measure the strength level of someone who's strength can increase? It's not possible.
And I consider these classes to be based upon physical strength, not the ability to affect gravity, magnetic fields, or manipulate energy. To me, these are different forms of energy projection.