He might not be. I'd say there's not nearly enough data to make that call.
However, it's fair to say, in a small sample, he certainly has produced like "one of the best hitters in all of baseball."
Wallner has accumulated 451 MLB PAs:
.251/.371/.523
.894 OPS
149 wRC+
Now it's not enough PAs. And he's been largely shielded from LH pitching.
But let's not pretend he hasn't produced.
He has. In spades. Like...one of the best hitters in all of baseball.
For the record, he looks pretty serviceable as a corner outfielder too.