Is a PD controller necessary if VBUS is always >5V?
If VBUS is always >5V, this device cannot meet USB specifications. You are sacrificing USB compatibility and endanger users who might accidentally connect a standard USB compliant device (with PD or without) and fry it. If you want to implement  "a board that will use USB Power Delivery", then implement the Power Delivery. In PD there is only one default and safe voltage, +5V. Anything else would be irresponsible hackery. If your source is permanent 20 V and up to 5 A, then it cannot be "power delivery", you should use a proprietary power jack for this.