I agree that 344 evolved is a high requirements
But
Raising up evolution dex isn't hard as you thought. With a sturdy magne (knows t.wave) + 4 Kinglers(easily catch in Dragons Shrine or Cerulean Cave) with F.S, you can lvl up and evolve almost pokemon really fast.
And I know, some people are scared that their Lati may not have right nature (or bad IVs or both) and think it's not worth the time and effort they've spent. But why don't you try your luck? Many people still proud of they failed legendaries (like me , an Impish Mew and 0x6 Azelf). Who knows how can your lati be, right?
Latios and Latias are the rewards for people who work hard with their dex, not for the lazy.