the block producers are the main token holders
That doesn't matter - even if the main token holders aren't the block producers, they can change that in a second. This is what happened with the Steem hostile takeover. It didn't matter that Steemit, Inc was never a witness - they controlled the stake so they controlled everything.
So what I'm trying to say is that we shouldn't worry too much about who the top voted validators are or how many, and should focus much more on the distribution of the token, which I think both SPS and HIVE do a pretty good job with especially compared to a lot of the other networks out there.
OK, that's the deciding point, I agree, and right, SPS is distributed rather diverse (there was for example no early mining etc.).
A sufficient number of validators to guarantee enough safety of the network (enough nodes) is reached by the option for everybody to buy licenses to run a node ... I still need to read more about the details, but am looking forward to see how things will finally work out.
As always: thanks again for all the time and hard work you are investing into the success of Splinterlands!