Difficulty set by pools
No, you see the difficulty of a pool is lower in order for the pool to be able to verify that the miners are actually working on a solution. The shares a miner obtains are mostly not valid blocks, which is what gets rewarded in Bitcoin, paid out to the pool and then paid to the miners.

The difficulty to create a block is not influenced by a pool's share difficulty, hence the total payouts the pool makes does not change, and old hardware is just as (un-)profitable.