You are doing wildly too much damage.
A ranger's damage shouldn't be out of line with the other characters. While some classes and weapon choices hit harder than others, it shouldn't be more than 20% or 30% higher, let alone three to five times the damage. So how is this happening?
Well, you should be able to see for yourself by asking how much of that damage is coming from anything in your class description or base weapon damage, and how much is coming from poison.
I can see at least three weird things going on here.
First off, that weapon is way too good for you. Magic weapons of the "very rare" rarity should be showing up in the 11th-16th level range. Your first Very Rare item may show up between levels 5 and 10, but it'll be what Xanathar's Guide refers to as a "minor" item -- an expendable item or non-combat magical tool, like a potion of speed or a portable hole. "Very Rare" weapons are the province of high level play and can be extremely unbalancing at lower levels.
Second, always be very suspicious of homebrew magic items. While the rarity system is imprecise and often outright wrong as it is, this weapon is far stronger than any Very Rare item. The Poison Generation quality alone is much better than most very rare weapons.
For example, look at Frost Brand and Flame Tongue. It's often said that these two had their rarities switched (I won't go into the analysis of why), but this Venomous Bow is better than both of them put together. Even on a success, the target of a Venomous Bow takes half of 5d6, or 9 extra damage. Consider that -- worst case scenario, your target takes extra damage from the poison effect alone that's equal to your other party members' total damage per turn, and that doesn't even consider a failed save!
And fail they will, a lot more often than the DC suggests, since the bow is also giving them disadvantage on the save. But the party doesn't stop there because they also become poisoned, taking disadvantage on attacks for the rest of the fight. The fact that the author refers to this poison as "mild" makes me instantly doubt their judgement.
Third, leaving aside the question of whether you can even apply two poisons to an arrow at once, that Bane poison is also crazy. It's vastly superior to almost every official poison; even if the dice are slightly smaller than the very worst the DMG has to offer, the save is enormously higher, and somehow Bane poison ignores resistance and immunity so you can even poison a stone golem. Whatever, that's broken beyond belief but I won't even get into it.
In general, one of the major balancing factors of poison is that it's a one-shot effect (or three, if it's arrows). By giving you powerful poison that comes out with every single shot, yes, you're doing way too much damage. It would be too strong even if it was just basic Serpent Venom on every shot. The fact that it also gives disadvantage on the save and cripples anyone who survives the hit means you're just a one-man show at this point. That item is insane and your DM should already know that just by watching you play the game.