Okay. In response to many suggestions/comments I've done some work on this.
First, for posterity, below is a full reckoning going back to 2014. Understand that the intent of this is to get a sense of the progression of different points in the season. It's kind of like an enthusiasm scale. So when lots of players are signed at the same time (e.g., expansion draft), I just stacked them up, even though that pushes them well past the date they were signed.
Unfortunately, this makes the whole thing look really misleading by comparison when 2014 and 2015 are included with later years.
So below the full history chart I have included a chart that is just 2016 through today. This will be the one I continue to update. I've eliminated the subjective "high priced player" shading and now only designate DPs with the green color. I welcome any other suggestions for what to demarcate.
And the cleaner version with just 2016-2019: