Without the attack-then-switch-to-shield option available there’s no reason nerf it further. Billhook isn’t powerful enough and switching from two-hander to to sword and shield can be useful, but mostly in an adaptive way.
For more flexibility you need spend not just two perks, but you also need to aim for the appropriate stats and gear. Like, if you want to use the greatsword as a shield wielder you’ll need to put more points into fatigue than with a normal shield build, because you need the heaviest armour to survive while you’re using the greatsword, than if you were still using the shield. You also need to have enough fatigue to compensate for the fatigue hits you’ll take from getting hit more often. Those are points that are not being spent on something else. In return, you get more attack options under circumstances, that also leave you more vulnerable and therefore less reliable if you use them. Seems more than fair.
