Main difference is that Sigwit block size is 2MB as a result difficulty level for mining it is easy and hence transactions are fast.
There are no segwit blocks. And no, we don't have 2MB blocks.
You are talking about the SegWit
2x fork which should have happened a week ago. (The
2x stands for 2 times blocksize (2MB))
Bitcoin already adopted to SegWit address formats, to make transactions smaller (Which leads to lower fees per TX, since fees are calculated in sat/B).
But there hasn't been an adoption to 2MB blocks. And thats good. On-chain scaling is no solution.
@OP: There isn't a good reason to delay the SegWit adoption. But as its with everything.. people don't like changing habits.
Look at IPv6 vs. IPv4 for example.. IPv6 is available for years now.. But 80%+ in Europe/USA are still using IPv4.. Just because they are used to it.