Funnily enough I never thought Oasis were a great live act, their Glastonbury set in 2004 was shite and they've admitted themselves that they've never really pulled it off as festival headliners.
I reckon they could do a good job now though because I think if they reformed and played Glastonbury, it would be highly anticipated and they have plenty of hits. It's not like theyre an active band 10 years past their prime and promoting some shite album like they were for the back half of their career.
I think if they did it now, it would be in a very different context and really good as long as they didn't sound awful