Overload is from from the best class defining trait in the game, but it isn't an inherent negative. It allows you to make very powerful tempo plays in the early game. I would agree that if you are forced to play off curve that it doesn't work out that way.
I think the main reason people see overload as a negative is because sometimes you want to make a certain play, but you are overloaded, so you can't. But that's the price you pay for having a more powerful turn than you were suppose to the turn before. People tend to focus on the negatives so being overloaded feels worse than it feels good to make bigger plays the turn before.
It is more a psychological problem than anything. The mechanic is very balanced.
But the "more powerful turn" typically entails playing a minion (or two) that just gets wiped away easily or removing a minion with a spell, and then losing tempo on your following turn. Except for the 3/6 minion that gains attack, and the soon to be 3/4 totem golem, Shaman really has no minions worth playing with overload which give you a "more powerful turn." And let's be honest, most of their overload cards can easily backfire (crackle/lightning storm) or just are there to regain board or finish a game with spell damage.
So again that more powerful turn where you miraculously summoned a spell totem (or dropped thanos), to play lightning storm on turn 5 to hit for 3-4 instead of 2-3, hoping to kill off some 4 health minions screws you over, and now that 5 or 6-drop (fire elemental / emperor / drake / etc) sits in your hand being worthless as you have a pitiful turn 6 (where if you didn't Lightning Storm, you would have lost your 6-drop to a couple 1-drops).
I think the problem is it never really feels like you're coming out ahead with overload, merely that you're catching up to close to even then sacrificing your next turn to fall behind again.
So this more powerful turn with overload doesn't really ever feel that way, as it's merely a response to the board, not actually taking the board.
That priest's 4 drop, if it lives a turn which likely can, opponent shouldn't play any minion. Wild Pyromancer+circle of healing could buff it to +8 for example with two minions on board, 11 to face.
Nasty card to deal with, truesilver and deathbite can't kill it. You need to waste a fireball probably. Shredder's can't kill it without a hero power, better have a silence around or two or three, priests have many targets for it... It's like a soft taunt. It has stats of a 4 drop standard taunt too. Very good card. I hope everyone gets a good 4 drop so that we can retire shredder in every deck meta.
I have a feeling warlocks will really struggle against it.
This card can be bad against other priests though.
To change gears a little as the overload argument is getting a bit burnt out, this Priest card seems great, and the reasons you mention definitely showcase the threat it can become very easily. Even works nice with the Injured Blademaster combo if you can't get to the Blademaster early game.