Basically, you are correct, but "will be" is too strong. It depends on the situation at hand. "Can be" or "might be" is more accurate. Some processes are not simulated. They may be too simple or too complex. Sometimes your process data comes only from R&D or an existing plant; no simulation. Small chemical businesses or poor business units within a "megacorp" may not spend the money for simulator software.
Also, a lot of times there is recycle. Your process calculations may convince you to change the H%MB or PFD. Or, if there is no commercially available equipment that meets the datasheet requirements, you may have to go back to step one.
Good luck,
Latexman
Technically, the glass is always full - 1/2 air and 1/2 water.