The Watcher has seen 14 million, six hundred and five realities, and this team is the one that succeeds.*
We’ve already seen that Captain Marvel at full power is just a speed bump to Infinitron. Supreme Strange is pretty much the only character in the multiverse who can go toe-to-toe with Infinitron; the rest of the team are more or less just distractions. The fact that they are so weak and insignificant but also so difficult to kill (due to Supreme Strange’s spells) probably wrong-foots Infinitron more than dealing with a team of Captains Marvel and King-of-Asgard Thors and “reformed” Thanii and not-quite-Supreme Doctors Strange would. The Watcher’s plan, after all, was never to “win”, it was just to briefly separate the stones and trap them and Inifinitron, which this team accomplished.
*Just to be clear, not an actual quote, just riffing on Doctor Strange from Infinity War.