In a world where there is an angel who can bring people back from the grave, a talking gorilla who can figure out how to make a device to tether someone to a specific timeline (or something like that), and a dancing Brazilian man who heals bullet wounds via sick beats, you would expect that a robot that was designed specifically for war would be better at waging war. Fortunately for Bastion and all of his fans in Overwatch, roughly estimated to be some dozen people, the mechanical bullet dispenser is likely going to be getting some tweaks that would make it easier for him to survive in and contribute to your average game.
In short, Bastion will take 35% less damage from all sources, his Recon mode will essentially make him a poor man's Soldier: 76, and his Sentry mode will no longer be as precise as it is now, but his Gatling gun's magazine size has been increased by 50% (in other words, less reloading, more holding down the trigger). This effectively means that Bastion loses quite a bit of his effectiveness at mid-long range against human sized targets in Sentry mode, but he will still be fairly lethal against most Tanks and their barriers while being slightly less vulnerable to skirmishers like Genji and Tracer. These changes alone are probably not going to make Bastion a staple in every game of Overwatch, but it does make him a more attractive choice when fighting multiple Tanks, especially Reinhardt.
Speaking of which, the timing of Bastion's buffs seems to indicate that Blizzard is trying to make sure that the multi-tank meta will never be viable again, seeing as how one symptom (or cause) of those annoying times still exists. As almost everyone who plays Overwatch knows, Reinhardt is the only Hero in the game who can seal up chokepoints and make it almost impossible to launch successful direct attacks. Given that having another Reinhardt is the most obvious and direct counter to fighting Reinhardt, he is now one of the most ubiquitous sights in Competitive matches, with games often being decided by who can crack Reinhardt's shield first, at least in certain ranking brackets.
But, despite his ability to provide a non-conditional, instant line in the sand that has more health than Overwatch's entire offensive Hero roster combined and then some, most people would also agree that Reinhardt isn't necessarily overpowered; he just makes life significantly easier for a well-organized team. That Reinhardt currently doesn't really have any direct counters who can destroy his shield in a reasonable amount of time and live makes Bastion's newfound damage resistance rather helpful (purely by coincidence, presumably) if your team insists on going through Reinhardt's shield rather than around it. Of course, Pharah and Bastion encounters are also likely going to be much more one-sided as well, so it's not like Bastion is going to be such a hard, guaranteed counter to Reinhardt that he becomes completely useless. Either way, Bastion being able to live longer to destroy barriers and the like is a net benefit for the game as a whole, giving people more options to counter Heroes that are considered staple picks.
As one can imagine, Bastion's buffs would likely have a more noticeable effect on the lower ranking brackets of Competitve mode, where people are more likely to go with the obvious and direct brute force method of eliminating Reinhardt. Teams who rely on slightly more complex team compositions obviously won't be affected; in fact, they may even benefit from this as Bastion won't be as large of a threat in Sentry mode. Naturally, as with all of Overwatch's character changes though, it would take time for people to adjust to the new buffs and nerfs to really get a feel for how the meta will change, if it even changes at all.