"Control" is not the relevant test, market power is, and the prime test for market power is having the ability within some (even small) range to increase prices (or possibly more generally increase price-to-feature mix) without sales moving to competitors. Its not an easy test to apply, and its possible for more than one player in the same general market (e.g., smartphones) to have market power, or for a player that isn't absolutely dominant -- or even the #1 seller -- in a market to have market power in that market.
Without having done any kind of structured data gathering and analysis, my intuitive impression is that it is not all that unlikely that a finding of market power for Apple in the smartphone market could be supported, and that therefore anticompetitive leveraging of its position in that market to build a stronger market position in the smart watch market could be an antitrust violation.
Without having done any kind of structured data gathering and analysis, my intuitive impression is that it is not all that unlikely that a finding of market power for Apple in the smartphone market could be supported, and that therefore anticompetitive leveraging of its position in that market to build a stronger market position in the smart watch market could be an antitrust violation.