Although this might be true...
Solo play in the suggestion would still add up to 10% for no one dying.
So the only option to discourage solo play is remove the 5% or 10% bonus AND add 5% bonus split to no-deaths and no-your-deaths.
Personally, I think buyer beware should apply to teamwork. Players that care will care. Players that won't will hopefully be chastised by those that care and learn to play better. Players that never care and never learn will never receive as much xp and will eventually find themselves invited only into similar-minded groups.
The endgame results will be the same.