There are plenty of games with that that suck, so it can't be the foundation of what Souls-likes are.
I'm sure there are also plenty of games with exploration that suck, I don't think that really makes it a valid point. I can't speak to what soulslikes are, since I haven't played the original games, but a game can implement one element well and still fail at being an interesting game, which doesn't invalidate that element in any way.
Realistically, can't both combat and exploration be foundational elements of soulslike? I got the impression a big part is the way the combat works, usually involving a lot of commitment into your combat moves, with animations on attacks, dodges, heals, and multiple ways to be punished (and punish enemies), including plain damage, wasting items, wasting stamina.