Even when implemenrting a POW/POS solution as described, we still need a POW algorithm. There are two problems that together cause long gaps between blocks.
the difficulty is high, but the hash rate is low, due to a large pool (e.g. nicehash) withdraws it’s hash power.
currently there is no way to announce a new and lower difficulty before the next block is found, what takes a long time due to 1)
POW/POS mixture as described mitigates 2) while a good pow algorithm hopefully mitigates 1)
The short or very short time to block caused by the increase of hash rate has no problem like 2) and a much smaller probelm like 1).
as the blocks are found very fast the pow algorithm can adjust and announce new difficulties very fast.
What also needs to be remembered, is, that a time frame with long or very long time 2 block is required leverage the overall time 2 block. Without time 2 block rates > 1 minute the long average of all blocks generated would get smaller and smaller for every peak in hash rate causing an overproduction of coins.