DC is not bigger blocks
It is an additional op code (OP_DRIVECHAIN), the block size stays the same.
Read the BIP
Discussion
Yes, but the data ends up in other chain(s), which is effectively the same downside, which ultimately means that it can't be relied upon as a solution to anything
The whole point of scaling is to move the data off the main chain
I don't see how having data in a sidechain is different than having data in lightning node databases