Most other coins I've used that forked, you only had to download the blockchain from the point of split. you didn't have to do a full sync, the drawback was you couldn't use the old tokens in the new wallet. the drawback with bitcoin ABC is the entire bitcoin blockchain is a beast. 99 gigs. it's a monster and takes several days to sync a wallet.
Yes, many altcoin developers have taken some old version of Bitcoin Core as a starting point for their own projects. They've forked this codebase but have not forked Bitcoin's blockchain.
Bitcoin's blockchain is currently 477175 blocks long and 123.4 GB in size:
user@host:~$ du -c .bitcoin/blocks/blk*
...
123414136 total
Notice that with full, 8MB blocks, BitcoinCash's blockchain would grow this much by mid-November. I don't expect BitcoinCash's blocks will be anywhere near full but I think this observation highlights the BitcoinCash philosophy. Long term, the initial 123.4 GB is but a drop in the bucket.