I'm not saying it isn't profitable. It is profitable in a manner that the more capital or money you stake, the more satisfying profit you'll get from those percentages you see.
That's why you can already foresee how much you will likely earn from staking because of the APYs that are given for each of those coins. But, you have to remember that the market is volatile and if you're computing based on their $$$ value, it will eventually change.

You can, as long as it's not a locked contract.