I can relate to this - I have developed online (video) courses and having to distill knowledge down into the bare essentials was something I struggled with initially.

Armando’s answer is a good one - you should look closely at that.

I would add the following:
* You say you end up with long chapters when you try to create a course. That indicates that writing a book may not be so difficult for you. Your publisher/editor would work with you to cut out the fat, and so that part of the work will also be taken off you.
* If you do write a book it’s contents will be easy to convert into a number of training modules, if you still wish to do that after becoming a published author. The structuring of the book in partnership with your publisher would have clarified a number of questions about the specific problems you are helping people solve and the issues you can address.
* You say you’ve already got a huge trove of video material. So how come you sound as if you want to start from scratch again? Or is it that you don’t own the rights to the materials you’ve done in the past? Simply repurposing the existing videos (breaking them into smaller videos and perhaps adding some commentary to update the material or provide further context) sounds like a very quick way for you to get materials out with little effort while avoiding the temptation to ramble.
* The medium often determines the message format.
— Udemy and Skillshare are good if you don’t have your own traffic, but you can’t put the same format on both. Udemy works with lectures that are 5-10 minutes in length, while Skillshare tilts towards 2-5 minute videos. You sound more like a Udemy guy!
— If you have traffic already then I want to assume that you are already conversant with all the good stuff you can do with Youtube. If you want to have your own platform to which you can direct your traffic I’d recommend Thinkific. Teachable is good too though.