Tritium isn't the concern. Fusion reactors consume deuterium and lithium. The sun doesn't have much of either. If you consumed all the Deuterium and Tritium in the solar system, you'd only get the equivalent of a few thousand years worth of the sun's power output. You also need various exotic materials for the reactor construction. Just matching earth's current power generation requirements, for example, would probably take more beryllium than exists on Earth.
Fusion reactors do not produce more power pound for pound than photovoltaics. ITER, for example, will produce 21 watts per kilogram, space based solar panels produce about 200 watts per kg. And again, if you were to place a fusion reactor in space, you also need the radiator panels as well.
Looking for dyson swarms is an accepted part of the search because it's something we expect to find. We knew about fusion long before the dyson sphere was posited, and everything we've learned in the intervening decades has made fusion reactors look less appealing.