YouTube videos come with 2 types of subtitles.
1. Pre-Uploaded: Where the subtitles are uploaded manually by the video creator.
2. Auto-Generated: Subtitles that YouTube automatically generates for the video uploader.
Mostly, the content that comes out as un-formatted or without any punctuation is because the captions for that particular video are auto-generated by YouTube.
If you use a video with pre-uploaded captions you will get content with proper grammar as well as punctuation.
We are looking for ways to add punctuation and auto format the text that comes out this way. Even though we can't give you a date as to when this will be available, do know that this is high up our priority list.
P.S. Not all videos with pre-uploaded captions will contain punctuation and formatting.