There's tons of MagSafe battery packs for iPhones. They charge the phone continuously. There's no need to let the phone drop to zero before attaching the battery pack. There's also cases with integral batteries. I assume there's Android equivalents for various phones.

I'd say these are more convenient than extra swappable batteries. They have integral charge controllers and charge via USB. There's no need to charge them in the phone or have to buy some extra external battery charger.

They’re incredibly wasteful due to inefficient power transfer which is a huge issue with wireless charging.

And it’s not just wireless that’s inefficient; with a usb connection you’ll typically lose at least 15% in a good buck/boost stage and there’s 2 involved in a usb battery pack: one in the battery pack itself to step up/down from pack voltage to the negotiated PD voltage, and then another lossy stage in the phone stepping down to 3.7v.