That nuanced, reasonable analysis may be the truth, but it's not the official line from the yeast lab, probably because they think (correctly, IMO) that most people are too dumb to hold a nuanced, reasonable opinion.
The reason people have problems with their package size is because they say specifically that pitching 100b cells into 5 gallons of 1.050+ wort is a "professional pitching rate." I'm not aware of any literature pertaining to professional brewing that suggests using <0.4m/*P/ml is an acceptable pitching rate. I'm not aware of any professional brewery that is using that little yeast, but I could be wrong.
The Activator™ package contains a minimum of 100 billion cells in a yeast slurry.. The Activator™ is designed to directly inoculate 5 gallons of standard strength ale wort (1.034-1.060 SG) with professional pitching rates. For lagers, we recommend inoculating the wort at warm temperatures (68-70°F/ 20-21°C), waiting for signs of fermentation, and then adjusting to the desired temperature. Alternatively, for pitching into cold conditions (34-58°F/ 1-14°C) or higher gravity wort, we recommend increasing this pitching rate. This can be achieved by pitching additional Activator™ packages or by making a starter culture. Please see the Pitch Rate section for additional information."
Very good point. I'm sure from a marketing standpoint, "Buy our expensive vial of yeast that's almost enough for a low gravity beer" is a non-starter. So whatever size they decide to sell, they probably have to say it is enough. I've love to hear their off-the-record opinion of this.
Somebody should organize a trip to the tasting room at White Labs and find out what their pitching rates are for the beers they are serving.