I believe that this is not the case in FCFF & EV valuations, as there's no effect on how the FCFF is distributed if we exclude tax impacts. I would say that if the Terminal Values in your FCFF models account for huge part of your EVs, the models are still unreliable. This is the case of many LBO modelings where revenue growths are modeled only up to 5 years and also to be low single-digits.
In the case of high-growth startup modeling, it's important to project FCFFs up to 10 years or 20 years until the company hits maturity. If after doing all this a significant portion of the EV still comes from Terminal Values, then this model is just as unreliable as a 5-year LBO one, if not more.