I'm not sure about the last advice. I suspect the last person was INFP/INTP (they LOVE criticizing ENTj's whenever they can - it makes them feel better about themselves

)
Sharing the leadership role? I mean

It's a tough world out there. You have to be strong and take challenges head on. ENTj's are great at that. Basically the "guest" is asking ENTj's to stop being ENTj's and behave like... INxP's. He's asking ENTj's to stop being strong. I believe ENTj's should not listen to this advice.
With all good comes some bad. We have the positive aspects of our faults. There is no "perfect" personality. You have to be willing to compromise certain things for others.
The ENTj qualites of enthusiasm & decisivenes, might come off terribly annoying to some people in a conversation. People who haven't got the same strength and energy as the ENTj might get tired with him. Yet, if the ENTj adapts and starts being "mellow, considerate, etc". not only will he lose the first 2 qualities temporarily, but other people will have more power over him.
A Leader, by definition, will be someone trying to "force down" his views about things. He will be someone who has to be decisive. He has to KNOW what to do and be SURE about it. No self-doubt. You see, ENTj's are people of ACTION - they want to get things done. They don't just sit for hours and think about things that have no practical use, and that will bring them nowhere - just to arrive to "logic". They have a practical mind. "Will it work?". This, naturally, comes at the expense of other attitudes. But it's the price to pay.
I'd say ENTj's should never lose sight of their strengths. They shouldn't start changing themselves too much for other people. We only have one life. There are lots of people who will appreciate the ENTj for what he is and what he has to offer. I think ENTj's should choose those people well. Or as Smilingeyes said, have a large circle of friends who don't expect too much from him. ENTj's are very principled people that can be counted on. Alot of people value highly this quality. They shouldn't waste time with people who won't appreciate them.