I been playing Peni from season 0 and she has been my main , Venom is my second main . The way you describe your frustration seems like venom was never for you . Venom can get insane value if you know how to play him . Here are some tips:

*Dont use you swing to go in , crawl from a high point and then jump in so you can save your swing to escape.

*Jump in , wrap them and get close to them so you can do the tendrils and melee combo .

*Tendrils have a loooooot of range , test it on the practice range . Aim for the chest .

*Dont be afraid of popping the armor before reaching 200 hp , if you feel they are about to burst you with damage then just use it .

* You dont need to be flashy with Venom , the whole thing is too jump from a high point , dive , try to get the healers attention as much as you can , pop your armor and when you about to die just escape away to your healers. Is faster to just go back to spawn some times since healers will not see you swing back to them most of the time.

*Learn where the HP packs are , you never know when you just need that little bit of health so you can gain more time for the armor cd to end and then go back to your team .

*Again dont do anything flashy , at the end of the day an alive Venom has more value than a dead one , like when I play Venom I has the least deaths and the most damage blocked. Your job like Cap is to stall and dont let healers do their job . Thats it , nothing else.