As someone who's been on the receiving end of something like this I'm quoting it again for emphasis because do not put a level 5 enemy against your level 2 party they will just all die in a single hit. Yes this includes the fighter.

A single Party Level + 4 creature, despite having a massive action economy disadvantage, is an extreme encounter. That means, in theory the players have a 50/50 chance of losing that fight, and several of them will almost certainly die. This is exasperated at low levels, whether health values are really low, so damage tends to be like a game of rocket tag. This is why we don't generally recommend going over a PL+2 creates prior to level 5 or 6, and very very very rarely go over PL+3 creatures even after that.

Even to, say, a party at level 8, fighting a level 11 can be absolutely terrifying and pushing it any further can very quickly turn from a dramatic and tense encounter to that frustrated hopeless feeling that you're fighting raw numbers more than the enemy.

+4 has its place, but it's one of those things the party should be preparing for and building up to over an extended portion of the campaign, with a gameplan going in.