I can understand how you'd have that point of view, especially given the Vietnamese who run over to the West would give off that impression.
Go over the Vietnam, however, and speak to anyone on the streets and in the villages. It's an entirely different picture. You thought Flips were obnoxious about glorious Flip Banana Land? Wait till you speak to a Viet nationalist. You'll want to gouge his eyes out, then yours for having suffered through all his verbiage.
The current Viet administration is suffering under the weight of War's legacy and the failures of communism. They're more than happy to take aid from the suckers in Congress who're so happy to give it away and still suffer from Nam guilt.
There's not very much information online that details the weakness of Chinese technology and equipment. The Chinese are very tight-lipped about what they can and cannot do, but if you've interacted with some of their defense specialists and military officials, there are subtle hints that all is not well. You can start with Jane's for an idea of their numbers:
janes.com/article/search?query=China
indexmundi.com/china/military_profile.html
A 2009 report to Congress has also raised the issue of the PLA attempting to modernize its forces and develop longer range strike capabilities:
defense.gov/Portals/1/Documents/pubs/China_Military_Power_Report_2009.pdf
The same report also mentions that Chinese military thinking and command is still stuck in the 80s, but they're moving on very slowly.
If it ever did come to blows, we might see some very high-tech equipment being field along side early millennium ground tech. Their logistics capabilities are also not as well-developed as the Russian's or the allied forces' during the First Gulf War, but as they will have homeland advantage in a land war in Asia, this is somewhat mitigated.
Hillary is a Washington apparatchik; she'll continue the same course to failure as Obama has plotted. This means she'll try to play appeasement to China due to the trade vice they have on us (and her taking an opposing position to DJT).
This will resultantly piss Japan and Vietnam, and potentially Korea and the Philippines as well. This situation, as you might imagine, is totally untenable in the long run, as China will desire more and more to prop up its slowing economy, and the US will get angrier and angrier. I cannot say for sure that war will break out between the US and China directly, but due to having so many already hostile players in the region, it will lead to a cataclysm where someone throws the first punch and things start blowing up.
Trump is a different player altogether. I'm voting for him because he's the best hope we have of changing things, but in the defense world, you quickly learn to never commit to any predictions past 6 months and never to trust platforms on defense commitments.
As he's said, he'll strengthen the US military (hopefully by strengthen, he means make it less bloated and more focused on fighting), and avoid participating in any conflicts that do not present a direct interest to the US. A war between China and Vietnam won't be of paramount importance to DJT, seeing as he doesn't want China to be in a stronger trade and economic position above us. In order to remind everyone that the US still has Asia-Pacific interests though, he will probably put a few carrier groups in the region to remind China that everything else is off-limits. The Chinese are notoriously cautious in war when it comes to anyone but their historical enemies.
Best case scenario would be a President Trump reviewing all the "traditional" alliances in the region and being as offhand as possible. We're ripe for a WW1 implosion in the Asia-Pacific, and the US will have to hedge its bets very carefully. If the US decides to prop up Vietnam, it'll mightily piss off a lot of other countries in the region like Thailand and Indonesia. China will have to be worked with carefully, especially given the "trade war" that might break out when Trump is President. Some old allies may have to be sacrificed, e.g. Taiwan, the Philippines, Vietnam, in order to maintain the balance of power.