All shares are not (worth) the same - you get rewarded more for shares worked from a more difficult computation - the difficulty is set by the pool, unless you have included a difficulty setting in your mining software - the pool will decide what workload is best for your card working with the workload it needs to perform.
EIP-1559 will not effect hash rate as such or the ability of your hardware to perform in any way - we just get rewarded less as the auction for gas has been ‘capped’
You may get more shares on another pool - but they will pay less per share
That said - I’ve swapped from hiveon to flexpool this week to give it a bash - seing as they pass on 10% MEV - hive only 1%