MechaTarrasque
Hero
Are we presupposing the absence of feats?
I envisage two weapon fighting to be quite offensive and really no more beneficial for defence than wielding a large weapon like a long sword for example (getting inside a long weapons reach is not an aspect that d&d represents in mechanical terms).
If I were to run two weapon fighting and great weapon fighting without feats i would simply change the following:
Two Weapon Fighting
- when you use the attack action on your turn, you can make one extra attack with your off hand weapon, provided it is light
- You may use your ability modifier to damage on all attacks
Heavy weapon fighting:
- You may add DOUBLE your strength modifier when you hit with an attack with a heavy weapon.
These up damage somewhat, but no more signifcantly than high level spells start ramping up damage.
Two weapon fighting becomes strong at the start, but also noting that without feats you can only ever use light weapons, this bith mitigates the attacks vs heavier weapons but also puts it as a viable fighting strategy, particularly for rogues to get a second chance at sneak attack.
Heavy weapons gain a boost to damage mostly to put thwm in a space of "hitting less often, but hitting hard" vs two weapon fighting.
He did say that feats would be addressed later-"Note that at this stage I’m ignoring the effect of feats, will get to those later"