When you face lex, try to stay at range as you can deal morde damage to him from range, if you're a skilled player and keep rolling, you may have the upper hand on him, also knock him back prenvents him from escaping and impact his aim.

Lex has more health than you. He has more damage and shoots faster than you. He has more combat-ready mobility to chase you down. His ult is suitable for duels. To beat a Lex shows how much more skilled than him you are. Good luck.