Would these two(three) not also be correct?

The character(s) on the blackboard is/are too small. The word on the blackboard is too small.

"The writing on the blackboard is too small."

Hei ban doesn't seem clear in the audio (sounds like ke yi) but in the above audio translation it is very clear. Is anyone else experiencing this?

I think I would probably say the letters on the blackboard are too small.

Singular should be accepted

The words are too small on the blackboard should have been accepted.