Most of the cast does not have plus on block 50/50's that have no gap, let's not pretend.
Some of the top tiers do. And some that have one like Shinnok for example still has other ways to do worse things like loop you. At least with Kano it may not have a gap, but on a lot of these starters after the EX Buff you have to move forward because the OH whiffs on crouch block unless you're righttttt on them.
Like if I do B31 EX BUFF on block, and I'm not steeping on your toes on block, the OH whiffs 10/10 times on crouch block if I throw it out immediately. If something is like "+ on block" but I have to step forward or do a lightning quick run cancel to land it, it leaves room for armor and backdash blowups. So they have to make a read on whether to block the low or full combo the OH.
The only starter I'm finding fully exempt from this and has clean plus frames where both OH/Low land without moving is F4~EX Buff.