Yup. That’s the cost. The benefit is much high spike damage.
I don't think it is actually...and I don't think it's worth it either. It's much better to have more higher level spell slots because then you can upcast your spells too as well as have level 6 spells which more than makes up for any power lost by not having the extra bonus action and you don't have that many metamagic uses anyway, they're a very finite resource so you just spend them all in two turns and then have nothing left to do without bonus actions and the fewer spell slots also means you burn out faster in combat.
