Going by common usage is the most sensible way to do it. Because the thing is, it doesn't matter if someone else had it chronologically; this wikia doesn't exist in-universe, it exists in our world as a resource to fans. And when someone mentions "Heero Yuy", 99% of the time they mean the protagonist of Wing who has appeared in numerous spin-off material; and not the martyred politician who exists almost exclusively in the backstory.
So to give the politician the vanilla name, or even just instituting a disambiguation page, means 99% of people are going to have to click an extra link to get to what they were looking for. Sure, you can say one link isn't that big a deal— but then, it's not a big deal to leave "if you're looking for the politician, click here" on the pilot's page, is it?
Lockon is an interesting case because the two people with that codename were both main characters, and both have equally valid claims to the name. So a disambiguation page is the right choice there.
In short: the current policy is correct and there's no good reason to change it.