Xypherous explaining offensive and defensive play in league of legends, he gets technical with the league of legends strategy etc.
Associate Technical Designer
However, the natural human reaction is to mitigate risk whenever possible - so typically, as players get more skilled - offering the choice between offensive options and defensive options - players will generally choose defensive options.
You have to seriously skew the reward structure between offensive and defensive strengths in order to counteract the basic human nature of risk aversion. Consider when top lane was about defensive play - defensive vs. defensive gameplay wasn't a contest - it's a truce where both parties agreed to just farm.
A player who chooses to incur risk needs to be rewarded. If you make the defensive option equally viable - then reactionary strategies are dominant. (In this case, dominant means preferred or more selected - not more effective.) This typically leads to stagnation as both sides adopt reactionary strategies but this means nothing ever actually happens - 'Cold War' type scenarios where two parties farm until innate character scaling overcomes player skill.