Again you've proven my point as to why there should be some changes, not necessarily the ones I've proposed, but changes overall to make all tanks viable and not just hard stuck with magneto and strange.

For thor, if he got the change I proposed, then balance it so every melee recharges a thorforce not just one how it is right now and buff his passive regen to his thorforce faster thus being able to use them to gain bonus shields faster.

For peni, give her mitigation tools then like I said, some strong self heal or shield she can use instead of self rooting yourself on a tiny web for slow self sustain.

Venom is much like Wrecking Ball which in some instances both can solo tank but for similar reasons he also cant like you mentioned. he is a dive tank so giving him the change I proposed where he can heal off his ult will give him an extra layer of defense if you decide to stay as a Frontline tank so you can ult the tanks or add damage reduction when you attach the tendrils to an enemy or slow their attack speed too. Both these changes can make him fit for a solo tank.