Here is what we know:
1.
https://www.stonetemple.com/eric-enge-interviews-googles-matt-cutts/
2. My ranking using only tumblr to rank has not vanished yet.
3. My ranking using some tumblr has not tanked yet.
4. A Meta Refresh works in many ways like a 301 Redirect, passing a high percentage of link juice. Especially with a 0% Delay, that acts almost identically to a 301. At least, currently. Just like a 301, a Meta Refresh is a way to get users from page A to page B. Nothing more. Having a Meta Refresh tag on a page DOES NOT mean the link is no longer Do - Follow or will be less powerful, it is a tool for Tumblr and with other websites, does not implicitly mean it will be worse for ranking.
5. Rumor is a 0 second Meta Refresh.
6. Again, 0 second Meta Refresh works the same as if not better than a 301 in just about all testing so far (Which you can Google) so it is not something to get your panties in a bunch.
So now that we have some facts and what we know out the way, what does this mean?
Using typical MMA math, or as we know if it SEO Math, if 301 passes no less than 90% of original link juice, and a Meta Refresh operates the same way reportedly and in practice, the Meta Refresh will pass no less than 90% of the link juice.
Those are fictional numbers, but just trying to put things into perspective. We do know it passes most link juice. Will it be less than a Tumblr does currently? I would bet so. Will it be significant? Not with a zero second delay. That is my opinion and until my ranking and testing shows me otherwise, that is how I will be operating.
go ahead and give up using Tumblrs. It makes it easier for me to get good ones. Until you test it and know it does not work, posting anything like this is a waste of time.
Me? I am having a VA prep a project now to split test a KW I have previously ranked to see if I can rank it the same way with Tumblr. We shall see. I suggest everyone does there own testing if they want to make it in SEO and not just toss around ideas. After getting a question in one of my threads, in PM and in email about this topic I thought I would share my thoughts.
My thought is, if it works still, does any of this matter?