It's not the same claim. The claim against Microsoft was that browser and OS dominance had killed competition ("cutting off the oxygen supply" of other browser makers) and was literally distorting the industry.

Browser dominance on its own was not the problem. The problem was that Microsoft's strategy was deliberately anti-competitive and monopolistic, and the browser was one symptom of that - not just because it gave MS massive market share, but because it created a technological chokepoint which limited the commercial potential of everyone working in the PC and Internet industries.

Remember, MS spent a lot of time and money promoting site/browser technologies like ActiveX that only really worked on Windows PCs, and seem to have been an attempt to look out everyone else.

It's hard to argue that iOS or Android are anywhere close to doing the same. Both may be walled gardens, and both have toxic effects. But they're not de facto standards setters, and they can't use their influence to kill competing products at equivalent scale. (They can and have killed or assimilated smaller products - but that's plain unethical behaviour, not clear evidence of monopoly. Taking steps to crush Twitter, WhatsApp, or Facebook would probably count as monopolistic. Killing SmallAppCo is just shady; sad, but true.)

If it was found that Apple and Google were colluding, that would be a serious problem - just as both had problems when it was proved they'd made secret agreements about employee mobility and salary negotiations.