It is not false advertising. Wifi calling is possible on a cellular data connection, if your data plan provider offers or supports it, so you can use FaceTime or Skype or any other VOIP service. All iPads are capable of wifi calling, and always have been. With my Google Voice account, I can make a phone call, over wifi, from my iPad Pro to anywhere in the world.
An iPad cannot connect to a cellular telephone service providers voice telephone network or system and nowhere does Apple ever claim it can. Since it cannot connect to a carrier's voice network, it also cannot natively send nor receive SMS/MMS texts. It can natively use internet based messaging services like Apple's iMessage service. It can also be paired with an iPhone to share the iPhone's voice connection for calls or SMS texting.
See https://www.apple.com/ipad/compare/
The question comes down down to what your needs are. If you can live with solely using wifi calling, then an iPad could suffice (although using a data only device on a cellular data plan might not be very cost effective, depending on your calling usage). For many people though, it is not a substitute for an actual cellular telephone and cellular telephone voice service.
