In theory, you are right. Wi-Fi calling should solve call drop issues at home and/or office with Wi-Fi access.With wifi calling and texting why do you still need perfect service at home? I'm never on a cell service at home or work, where I spend the majority of my time.
In reality, however, Wi-Fi signals themselves aren't entirely reliable as you walk around, step out, or step into the Wi-Fi zone. And Wi-Fi is still at the mercy of your ISP.
iPhone 6 and 6 Plus's VoLTE in theory is supposed to be a lot better at transition, but in my experience, it still ended up dropping calls or causing garbled audio, either because the signals between usable Wi-Fi and LTE may be weak or takes longer to lock in.