You are saying that 8MB blocks are resulting in faster confirmations. However, BTC transactions would be confirming in the next block with low fees if the BTC chain was handling the same amount of transactions as the BCH chain. You are talking about the max block size, when what matters is the block size that's being used.
Furthermore, SegWitx2 having "8MB blocks" is not quite the same as a base block size increase. As Jimmy Song explains on Medium:
If there are no Segwit transactions in a block, this weight calculation collapses to size, but in the more general case of blocks with Segwit transactions, miner profit does not strictly increase with block size.
For this reason, miners are not incentivized to make a block the maximum possible block size. This is because after a certain point (2mb without segwit2x hard fork, 4mb with), miners have to remove transactions in order to make the block size go up as they’re likely already up against the block weight limit. That, of course, reduces fees and makes mining a larger block add cost for a miner.
In other words, you can expect miners to mine around 2MB blocks with Segwit only and 4MB blocks with Segwit and 2x hard fork.
For this reason, miners are not incentivized to make a block the maximum possible block size. This is because after a certain point (2mb without segwit2x hard fork, 4mb with), miners have to remove transactions in order to make the block size go up as they’re likely already up against the block weight limit. That, of course, reduces fees and makes mining a larger block add cost for a miner.
In other words, you can expect miners to mine around 2MB blocks with Segwit only and 4MB blocks with Segwit and 2x hard fork.
