i don't follow the details of all these shitcoins but it doesn't look like a 51% attack, there is no reorgs just some group that had a little amount of hashrate and decided they wanted to create a new shitcoin (bcashabc) out of an existing shitcoin (bcash) just like another group did and created another shitcoin (bcashsv) a while back. each with different consensus rules and mostly incompatible chains.
as i said before you can do the same exact thing with a single CPU too.
It's a DOS attack. All blocks are being kept empty by a single miner.
