The thing is people say he's underperforming, but he really isn't. This squad is absolutely AWFUL.
However, we clearly need a manager who is capable of overperforming and getting every single ounce of the players. Right now unfortunately it looks like Lampard can't do that, and it's a massive shame because he's been the one good thing about this club in the last year - not that I ever thought he was a particularly good manager, but he truly has bought into the club, understands the issues, and truly has tried his very best. Should be prerequisites but that's not always been the case at Everton, has it.
But regardless, Everton are down if they don't make significant signings in this window. One, at the very least, should have been through the door already. It's pathetic. And none of that is on Lampard.
I'd say anything above the relegation zone is acceptable for this squad, but being in the relegation positions is underperforming. 3 wins in 18 games is not good enough and I doubt even the manager would argue it is.
We've seen how this goes at Everton. Once the spiral starts, it doesn't stop until the manager is replaced, and the bounce is only short term too.