The issue with most workplace pensions is employees get signed up to a scheme with, say Aviva, and keep it in the default fund. That's always a poor performer as it is very risk free but sadly most folks aren't savvy about investing and just keep it in a 'balanced' portfolio fund meaning they get a mediocre result. You should be aiming for 10% return per year (which will be around 7% after inflation and fees). People will say 'you can't guarantee that' - well no you can't but you do have decades of data showing that's what an index fund should achieve.
Best to have it in something as closely following a global tracker as possible, then it will grow faster assuming a 10+ year investment window.
Also you get the personal allowance before you pay tax on pension withdrawals.