Based on my experience, I handle it myself.

I use, what I call, the "mirror strategy". I organize the campaigns as easily as possible so It wont be a pain in the butt to make weekly alterations.

I have two campaigns for most SKUs if there are too many. One auto and one manual. If there are not that many SKUs, I add a third campaign for ASINS. I call this campaign the Competitor campaign (which is manual).

I download keyword reports on a weekly basis and organize them in excel by campaign name so I know which keyword goes along with which. The auto campaign acts as my "keyword scraper" so I can see what people are searching for right now and what is working for me. If there is a keyword that is working, I move that keyword to the corresponding manual campaign I have already created (or competitor campaign if its relevant).

However, Amazon is updating this. There are some accounts out there that can keyword scrape from within the manual campaign...leaving the auto campaigns as useless and just a waste of ad spend. Amazon has updated this on some accounts where you can actually do it all from the Seller Central platform and you do not need to download anything. This is, unfortunately, not available for everyone just yet.

If this sounds tedious its because it is. An Amazon business is full time work. I do nothing else.