In a generic aRPG, do you honestly think that players experiment more when there is high respec costs? The answer is obviously no and basic common sense.
Unfortunately more common than you think there is none.
Things are rarely so simple.
All else being equal, it would be common sense that you wont have more experimentation with a respec cost. But not necessarily meaningfully less either.
More relevant though, all else are usually not equal, so people very well could experiment more in PoE even with respec limitations, because the game attracted people more uh, dedicated, lets call it that, to experimentation.
Not saying they are, but they very well could.
There is a door-shaped hole in a wall. Can I walk through it? Yes.
There is now a door in the wall with no lock. Can I walk through it? Yes.
There is now a lock on the door, but I have the key. Can I walk through it? Yes.
I do not have the key. Can I walk through it? No.
“But Sai, why are typing up such nonsensical gibberish?”
Because for some reason we still have people who believe restriction enables experimentation. In the above four states, let’s consider the act of passing through the door as an experiment. For 50% of the scenarios, there are basically no restrictions. Everyone can do it whenever they want, as much as they want. For the third scenario, the act of experimenting requires something else. This key manifests in the form of gold costs, alt rerolls, or concepts the player will inevitably have or not that means time spent or time waiting. Freedom is undoubtedly diminished and inhibited by the steps required to acquire the key. The 4th state is either a result of not meeting the qualifications for the 3rd or the game basically being all, “No respecs, period!” like early D2. I should remind that the act of passing through the door is the qualifier of experimentation. You can’t turn a No into a Yes without something vital changing.
Now, I’ll simply say that doors exist as a concept because humans realized that the ability to pass through walls is pretty handy. Indeed, we may try to litigate who is qualified to pass through a door, be it our personal homes, business, vehicles, etc… People trying to justify (steep) respec costs are dabbling in this same concept, but very frequently with the misguided notion that how other people pass through this particular door will be affecting them. They aren’t. This isn’t a physical process. Any restriction of digital goods is arbitrary, including cost to access. We can all walk through the same door at the same time, not at all, or any variation in between. You won’t bump into me. I won’t bump into you. We can run blindly or think carefully about each step.
Regardless of where you stand, the moment the door is locked, less people are going to be passing through. You can’t act surprised when a barrier for entry works exactly as designed. People will not experiment as freely. They will want to make their key(s) count. Adding that weight to the process of a build doesn’t automatically make the process of making a build better. All you did was put some rope lines in front of the door. Ever hate having to walk through those little mazes when no one’s around? Yeah, me too. So what makes such annoying RL time sinks okay on the net? And respond to that as a player, not a soulless corporate bootlicker with buzzwords like retention or meaningful choice.
I’m not saying it’s one way or the other. I’m saying that nobody can actually prove any claims on the matter.
Doors aren’t character builds, and you can make up just about anything to say “builds in Diablo are just like that!”.
Hell even in keeping with the doors, let’s say I put a door shaped hole in a wall in front of my D&D party. They’re gonna think nothing of it and just walk on past. They might check for traps, but that’s about it.
Now give them a locked door. They might try to pick the lock, search for the key, find another way around, or attempt to bash their way through the door. There is also a chance they’ll check for traps here as well. Removing the barrier basically funnels everybody into one path here.
We’ve even seen this in play in video games decades ago in games like Super Metroid and the old Resident Evil games. They’re designed around parts of the map being locked off to you until you figure out how to get past the restrictions, which led to players experimenting to figure it out.
Of course, as I said before: Doors aren’t character builds, and neither is locking off parts of the map until you have the special item that unlocks it.
The main concern for free respecs is the game getting designed around it, and the game expecting the player to constantly respec for content that is tuned around using a top end build.
I’d be curious to know how many people who want free respecs would complain if the even the highest end difficulty was tuned around a closer to average player using an average build.
It’d make the game too easy for people using optimized builds but hey, the concern would be addressed and then “if you don’t wanna respec then just don’t” might actually mean something.
The moment you add a door, and a lock, you might also make people more curious about what is behind the door and lock, getting more to attempt to pass through. Human curiosity is a strong force 
We are talking games here. Balance of powers, costs etc. are pretty fundamental to the experience of a game.
When moving a knight in chess, I have to move it in a cumbersome way, even though it would be faster and more efficient if I could move it in straight lines.
