Yes, it is completely normal. Not right, just normal. The brightness control ( the black knob in the middle of the center instrument cluster) is a rheostat that is notorious for going bad. You have a few choices:
The Italien tuneup method (scuzzi): move the knob back and forth through its adjusment revolution and hope you can find a good spot on the coil in the rheostat. If you are lucky, you will find a good spot and it will be near the brightest setting.
The "I don't care what it costs" method: buy another center instrument cluster and hope the rheostat on that unit works better than yours (the rheostat itself is not replaceable).
The elegant repair, which is to bypass the adjuster and hardwire the instruments on their brightest setting (search this board for other posts on that procedure).
Best,
Greg
'64 230sl, fully sorted out...ooops, spoke too soon