dPOS can do high volume big blocks in short time, that is why they are better for dAPP to operate. settlement layer require decentralized participation, tau is more focus on the "decentralized" part of the tri-angle.
it is complicated to debate how many miners are enough, i do not know either, how many TV channels do we really need? 8, 100 or a million?

Giving up high volume transaction numbers on main net is a big bet. Most of startup project dares not do that, but Satoshi did it through bitcoin in return for consensus. One blockchain to satisfy all DCS (decentralized, consensus and scaling) is impossible, there is math proof on that. One ecosystem of block chains can do that. Assume there is an ecosystem in the future, all we need to do is to pick up a position. TAUcoin picks up "decentralization" and consensus, which force us to run mobile mining and 10kb block size, no high volume as result.

I personally do like dPOS for application say social, commerce and search engine. dPOS needs great enterpreneur to build venture to fight current giants. I do hope steem can win, but it seems their product is loosing traffic and founding team is gone.