Yea , Boom looks like the weakest team there but after what we saw with Xtreme gaming we can say they are on the same level ...both teams are tier 3. If once again a Chinese team will fail to achieve something , then why they still bother with Dota ? because the only thing we can see for sure are 322 games from them and nothing more. 
I'd still say Xtreme Gaming is a bit higher because they rolled Execration, and during the EWC qualifiers, Boom couldn't even beat Execration. Despite the decline in the Chinese region, there's still money to be made in competitive Dota, which is why these teams continue to play.In other esports titles, such as League and CS, the gap is wider between each region, but the teams continue to compete.