Ovinomancer
No flips for you!
Improv just means you're writing it on the spot - unless you script your games, you are improvising them. So, really, you're saying that acting is not a universal part of a role playing game. Let's see what the PHB has to say about it:So, roleplaying is acting, and it is part of every aspect of the game. The tenants of good improve are absolutely relevant for RPGs.
Eat the Green Eggs and Ham folks. Try these suggestions to work WITH your players. You'll like the results.
As an aside: Another interesting thing for DMs to consider doing to improve their DMing - look up videos on how to be charismatic. While this will help you roleplay charismatic NPCs, it is not the reason I suggest it. A lot of these videos do a good job discussing how typical human interaction really works - and how to make a game fun for all your players. It'll help you with problematic players, and make things more fun for involved players.
Um, no. Roleplaying is not acting. The definition you posted doesn't say "acting" or any form of act anywhere. Roleplaying is the act of playing a role. That doesn't require acting. If you say, "Bob the Fighter swings his sword," that's roleplaying -- you're playing the role of Bob the fighter. It isn't, however, acting.
And, no, again, you do not have to charismatic to roleplay a charismatic character because, again, you do not have to act to roleplay. I can roleplay a charismatic character by saying, "Bob the Bard spins a wonderful tale about how heroic it is to slay dragons to encourage the King's army to stand against the dragons impending attack!" This is roleplaying. This is not acting.
Can you act? Absolutely, and a lot of people have fun acting. However, acting is sufficient but not necessary for roleplaying.