Polynomial time does not necessarily make it easy, the degree of the polynomial could be plenty high making large problems still sufficiently expensive.
It need not even be of high degree. With a large enough constant, even a constant-time algorithm could be way out of reach.
Suppose that somebody shows that, once you are past a googol^googol (not a big number, as numbers in mathematics go), factoring doesn't get harder at all, that would be merely a curiosity in practice (It also would be a hugely surprising result that would inspire mathematicians to start looking for ways to bring that limit down)
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Polynomial time does not necessarily make it easy, the degree of the polynomial could be plenty high making large problems still sufficiently expensive.
It need not even be of high degree. With a large enough constant, even a constant-time algorithm could be way out of reach.
Suppose that somebody shows that, once you are past a googol^googol (not a big number, as numbers in mathematics go), factoring doesn't get harder at all, that would be merely a curiosity in practice (It also would be a hugely surprising result that would inspire mathematicians to start looking for ways to bring that limit down)