1) The "PoS" percentage in miningpoolstats is a glitch that only miningpoolstats seem to have. If you check the diagrams from BitcoinZ explorer or Zel Explorer , you will see that there is no "PoS" percentage (and of course BitcoinZ has no PoS because it is 100% PoW).  We have sent emails to miningpoolstats asking to fix this or at least explain us how this "PoS" labeled percentage is there but nobody has replied so far.

 2) The circle of longer block times and then a few much faster blocks is a characteristic of every Proof of Work coin and it is related with the difficulty spikes.
 It can be seen in Tent, Flux, Digibyte , everywhere in an analogy with their average blocktime (for example you will see in Flux - with 1 min block time avrg-  one block being mined after 4-5 mins and some others being mined in 5-7 secs  or in Digibyte -15 secs avg- some blocks being mined at 1 minute and others at 3 secs).

The higher the hashrate is for a network, the more stable the averages are getting.

 3) The fact that BitcoinZ has many blocks mined by addresses that are not grouped in a pool, comes from the fact that it hasn't so huge network hashrate like Ethereum or even like BitcoinGold, so even a single miner that has more than 4 strong PCs can easily mine solo and hit some blocks per day or even better someone that rents a mining farm can easily get many blocks per day.
This is how the project ends having this picture and it is nicely decentralized to many pools, to many solo miners and to few mining rentals as well.
If more people join the pools, these "solo" people will start reducing because they will have lower possibility to "hit" a block.


I hope that I have helped to clarify these things