lest I can’t explain—nor would Lenin either—why Engels would say what he said.
In the democratic state the interests of the wealthy (as we now know through many studies) are getting more reaction then the interests of the poor (working class).
As such, democracy always includes class warfare (and battles between different groups that may not belong to a single class), may it be at the ballot or (more likely) outside, through e.g. lobbyism.