The mastery choice should be permanent. This is one of the design pillars of LE.
At the point when you stand next to the altar to choose your mastery and you are not sure what to build (and have limited time leveling) you should start collecting info about the masteries to choose.
You can read all the passive nodes to imagine what you can build. There are build guides for so many different masteries and different builds within the masteries. I don’t say “follow a guide”. But use the videos as a showcase of the class.
This decision has weight and should be made carefully.
Even if it would be allowed to respec your mastery at level 50# how would you do this effectively?
As a Druid you are a melee class that focuses close range combat and str as main attribute.
A Shaman is a spell/minion based mastery with focus on elemental (cold/lightning) damage and range combat.
The item choice is completely different. The game would leave you - a newbie that has no experience with the new mastery - with a lot of passive points and useless gear. On top you would have to change your skills and specialisation trees, too. You trash all your gear and skill progress.
I don’t think this would be a less punishing experience than leveling from scratch. It will leave you with a completely broken character, that isn’t able to progress the slightest bit.
For experienced players this is not that much of a problem. They would know what to do and may have items in their stash for a switch. But they wouldn’t have made a “wrong” choice either because of their experience.
I personally rather create a new toon than respec a build for a change. For example I have a melee VK and a caster variant. Because both of them have very different gear and skill setup (the passives aren’t that much different) it would have been a chore for me to change that build.
With a new playthrough you can grow into the character, skill synergies, passives and gear. You learn how to play and progress your build.
Yes, it sucks, if you end up with a character/playstyle you don’t like. But then you didn’t do your research, to be honest.
Just another advice:
Tell us, what is it exactly, that makes the Druid not feel good for you? Often new players make skill choices that aren’t most effective and so a class feels clunky, when there are ways to play a class differently. So maybe people could help you making your mastery being fun.
Cheers! 