Are they?
Well, they are and they aren't. I would rather say that playtesters are the question.
Don't you love this type of answer?
Let me explain. Playtesters are crucial to any game design. With balancing issues at one end of the spectrum and the feel of the game at the other end, playtesters can help with it all.
So let's say you're playtesting your game. It is not the first time it's being played, it's somewhere in the middle of the development work. You were there to see the playtest, but did not play.
The first thing you want to do is write some things down during the game. See how players feel and behave. Are they engaged or looking at their phones and watches? Do they have exciting moments? Here I would suggest writing things down in the form of a question, like:
How do I make the action X more appealing?
How do I keep players in the game during downtime between their turns?
How do I make the drafting quicker? and so on...
Keep those questions to yourself (and co-designers, developers, and anyone who helps you design). At least for now.
At the end of the game (assuming it works ok and ran until the end) try to extract the information from your playtesters. When doing so, playtesters are divided into two types: the problem giver and the solution giver.
The problem givers will tell you what bothered them, you can ask them a few questions until you reach the heart of the problem. They are very important, because they help you understand what is wrong with the game.
The solution givers will tell you what you should do. What I try to do is turn them into problem givers. This is a very important step because playtesting is the step where you find the issues. After you go back to working on the game it is time to find solutions.
Don't get me wrong, I sometimes playtest with good and seasoned designers and I write down every suggestion they have. Sometimes a random gamer will give you a piece of thought that will improve your game no end, but this is the second layer of what I am looking for while playtesting. If that second layer overshadows the first layer, which is finding the problems, you might get stuck with a set of solutions to problems you did not identify.
Even after the game, when asking the testers questions, write things down in question form to yourself, like:
What can I do so that X is less fiddly?
What should I buff to make strategy X more balanced?
What parts can I change to make the game time shorter?
Why did the bidding felt out of place? Should I replace it with something else?
So, are playtesters the answer? Sometimes they are.
The only thing you need to be sure, is answers to what issues?
Design more, playtest safely, and have fun! Pini!
In the image, the answer is clearly yes, but does she know the question? (she does)