I think it will be best to accept the mid $xxx offer.
If you have not stated that you have received mid $xxx offer for this domain,
I would have appraised it as mid-high $xx end user.
The new extension.wtf is unknown to many and unpopular.
There is no chance that this domain can be sold for $x,xxx.
The keyword "art" with .wtf doesn't make any sense to me.
The extension .io is popular and familiar to many developers and companies and thus some .io domains reach mid $x,xxx to low $xx,xxx.
For this reason Art .io was sold for $6k.
A website developer or company can develop Art.io in many good ways.
Also .io ccTLD rank very well in searching results.
You can know for sure the domain was sold based on whois change and the addition of $x,xxx to the seller overall sales, this kind of data is only available after a few days(In case the Sold by auction is not good confirmation for you).
Same for .info, Art .info domain is worth $xx,xxx since the gTLD is known and popular and the .info=information makes sense with the Art.
Good luck
