If you drop armor and speed, what's it's purpose then? Wouldn't it be to slow to be a cruiser killer, and risky as a Panzershiff chaser too?
It is not meant to be a Panzerschiff killer (or even cruiser killer). It is meant to be a Panzerschiff analogue, but French.
That 17000 ton Dunkerque ancestor seemed to be the best idea for that to me.