In my experiences:
A good ruleset can make an inexperienced GM worth playing under.
A Bad ruleset will make an inexperienced GM completely annoying.
A Good GM can make any system playable.
A Good GM with a good system is playable and not a stress source for the GM.
A Great GM can override any system and make it fun.
Most of the people who claim "System doesn't matter" are not GMing... The game systems job is to make life easier on the GM.
A good ruleset can make an inexperienced GM worth playing under.
A Bad ruleset will make an inexperienced GM completely annoying.
A Good GM can make any system playable.
A Good GM with a good system is playable and not a stress source for the GM.
A Great GM can override any system and make it fun.
Most of the people who claim "System doesn't matter" are not GMing... The game systems job is to make life easier on the GM.