I've been informed that "Pantser" as a term comes out of things like NaNoWriMo. There as little planning as possible makes sense.
But outside of a strict deadline like that, choosing to not planning at all is just a bad idea. It's way, way worse than over planning.
When you first set out on a project, whether comic or novel, there are no deadlines. It's one of the rare times you have the true luxury of time. So why wouldn't you take advantage of it while you have it? Choosing to not plan is squandering a massive opportunity.
Planning isn't restricting yourself. It's making a map and setting up most of your supplies before you start creating. It's like when you're making a big, complicated meal. If you go in trying to remember the recipe off the top of your head (that you read once but never made before), and grabbing your ingredients out of the pantry only as you need them, it all goes wrong. You didn't have one thing so you had to substitute something you THINK might be right. But while you were searching, your food started to burn and you forgot to preheat the oven.
Where as if you do just a little planning.... You have the recipe there. You lay out your ingredients so they're easy to grab--going to the store to get what you're missing. You chop things up first, so it's all ready to go. And it all goes much more smoothly. Now it just depends on your skill to execute it, not your ability to do everything all at once.
In making comics, your recipe is an outline. Your ingredients are your cast. Chopping things is character designs for at least your main cast. Missing ingredients is research that needs to be done. And like with cooking, you can still improvise and go off-book when you need to. But at least you know what your next steps are.
And far too often, people don't want to stop in the middle of writing to do a bit of research to make sure they have their facts right. So they just make it up with what they remember and it really, REALLY shows.