Android, however, still holds the largest share of the United States smartphone operating systems’ market and has done for many years. Vendors Samsung, Motorola, and LG have all adopted Android as their mobile OS and sales of their devices make up around 50 percent of all smartphones sold in the United States. Sales of Samsung smartphones alone account for 28 percent of the sales market and this could rise in the future with studies showing their Galaxy series of devices rank highly for customer satisfaction among Americans.
Care to cite cases in the modern era? Every time someone tries to find citations, it’s always multiple companies colluding - which is always illegal.
You're right, according to your source, Apple has 52.4%. Apple also has the majority of mobile app purchases in the US, as well.
Even if they had less, companies have lost antitrust lawsuits with much less than 50% of market share.
Further more, both Apple and Google have a duopoly and are guilty of engaging in anti-competitive behavior.