Six mana can be a bit steep, but the ability to play this regardless of your meta game and know that you can slow down power creep, slow down aggro decks, slow down graveyard pullers, people leaning into enchantments, artifacts, equipment, etc
The natural instinct against poison is to let yourself get a few counters early on, and then win on the back of your bigger and better creatures
You might find someone else who says Whoa, thats neat
Even if your deck's game plan does not revolve around such tactics, the value these spells bring to most decks gives you options , especially as the game goes on
toss in a kicker cost to protect everything and you have a super impactful card
Delney costs three for a 2/2 Scout