40 is a lot when you go into the grand scheme of things.. people started armor mixing for similar bonuses.
it only sounds small when you put it in a vacuum like this, but that damage is dealt on top of the already existing damage dealt by the weapon. i'm too tired to get into much higher detail right now (i want to make that lovingly over-detailed calculator at some point but i have been Insanely Busy) though since i'd probably be wrong but an extra 40 dps is akin to an extra 2400 per minute which is... substantial to say the least, when thats something like 5% of the lunatic cultist's hp on expert.
of course this is also getting to be in a theoretical world where defense doesn't exist, and that extra damage starts to matter a lot more when it does lol. realistically though this probably doesn't matter too much since this is ultimately a PvM game that borders on power fantasy - especially at the point of the game this would matter in - but it is still a much more significant increase in damage dealt than it initially seems to be
realistically speaking i otherwise don't feel that strongly about this, it's a substantial change but it's not substantial enough to ruin the game's balance when at this point in the game everyone has access to infinite flight and almost everyone has access to a screen-wide damage button that ends up turning encounters into just kiting around the world unless you're in a hyper-specific setup or challenge run. whatever is the most fun is where my allegiance lies. the average player is NOT mixing and matching armors for maximum dps, they're just putting full shroom on and pew pewing or using hallow for the rest of the game.