Word for a person who talks without content

Gasbag (slang) - A person whose talks are devoid of content, i.e., gaseous.

TFD - One given to empty or boastful talk.

Not sure if it's what you're after, but you could try "rambler".

ramble

• to talk or write in an aimless way.
• (of speech, writing) to lack organisation.

As far as a diagnostic search term, logorrhea may be most appropriate. From Wikipedia:

a communication disorder, expressed by excessive wordiness with minor or sometimes incoherent talkativeness.

A related search term could be aphasia or aphasic, which refers to a general class of language disorders.

As for precise usage, the verb that comes to mind is bloviate. From Merriam-Webster:

to speak or write verbosely and windily

I would offer blatherskate or blatherskite :

A voluble purveyor of nonsense; a blusterer.

Nonsense or blather; empty talk.

Blatherer

blather at Merriam Webster:

to talk foolishly at length —often used with on : Old Norse blathra; akin to Middle High German blōdern to chatter First Known Use: 1524

Blatherer at Collins:

someone who blathers