First of all....sorry that you are not having fun.
I've actualy played this scenerio solo a couple of times... to get a feel for it.... and I believe the PDRC is a VERY viable power. It's a little slow getting started out of the gate.... but it's got alot going for it.
I don't think I'm mistating it when I say in the first test game we played China (Grymme) is pretty much mopping the floor with the US player.
Some observations if I may... and please don't take this the wrong way. I actualy intend this to try and help you have a more enjoyable experience... even though it will make my road a little tougher.
I believe you've done a few things that have severely handicapped you as the PDRC.
1) You've pretty much thrown away your air power. Although China starts with a tech disadvantage in the air....they have a pretty decent sized air-force and certainly can at least contest the asian air space with the USA....and can even achieve dominance if lucky. However, you are using your air in penny packets.... 2 or 3 fighters and 2 or 3 bombers in a group....and only one group assigned to a single mission. This is a pretty sure way to loose your airforce unless you have total air dominance.
For example, say that you have 12 fighters and I have 12 fighters.... but you send those fighters at me in groups of 3, one group at a time... they are going to get totaly shot up...because I have 4 to 1 odds in each of those fights. This is pretty much what you are doing with your air.
Even where there are no intercptors... if the enemy has flak guns....and you send your air attacks in small groups rather then bunched....you are giving the enemy flak alot more opportunities to shot down or surpress your planes.
Part of the reasons you are not doing so well is that your air-force isn't really being very effective in supporting your ground operations in key areas (like Korea).... conversely you are not doing much to contest my air-force from knocking out your assault troops.
2) Your ground operations are also hindered by the fact that you are not taking advantage of concentric attacks. The attack you made against Seoul on turn 5 is a perfect example. You sent alot of good troops in...but they got absolutely massacered... why? There was an unoccupied mountain hex next to Seoul that you could have moved into to attack from 3 sides(even if it meant a turns delay)... but instead you attacked only from 2 sides. The difference between an attack from 3 sides and 2 is huge....not only can you jam about 50% (I believe) more troops into such an attack...but the difference in the attack bonus is more then double as well. It's not such a big deal when the enemy is in relatively indefensible terrain or you have huge odds against them...but when attacking a well prepaired defense...a concentric attack is almost a requirement. Had you hit Seuol from 3 sides that turn instead of 2 (especialy if you were able to soften it up with air, artillery or shore bombardmemt) you had a decent shot at taking it...rather then getting slaughtered.
3) Burma can be a bit of a slog. PDRC really needs to bring thier engineers along there to build a road through the pass and speed up movement... but you can do well there.... use Partisans and purely foot mobile troops to occupy the high mountains on either side of the pass...to open up concentric attack.... make use of air and artillery to soften up the enemy....and don't forget your para's and using air transports from your HQ's to do air supply missions. You actualy aren't doing bad in Burma.
4) Given it's position... the PDRC really needs to be quite a bit of a naval power as well. It's got pretty decent starting naval forces as well. Although the US has a larger and more able Navy it is far more spread out...and has more areas it needs to commit to... China actualy can get a local naval advantage against the US early on. However, you really haven't done much with your navy so far.... you've left it out in penny packets (especialy the subs) for the US 7th Fleet to take on and destroy piecemeal before running back to the safety of a protected harbor. Note that even though you have far more naval assets in the area...I've won every naval engagement so far....because I've faught each one on MY TERMS. I find a small group of your ships, close to where my port is....I run out, hit them once....then run back to the safety of port before you can retaliate. You keep letting me do this, I am going to wither away your Navy.
Leaving your navy out to sea can be very risky. If you do it...you want to make sure you stack them in big enough groups that it is risky for the enemy to attack...and when they do, they'll use up all thier action points...so they can't just run away to safety after the fight.
Also, you've given me no reason to force an engagement with you. Naval shore bombardment from capital ships can be devastating....you haven't done any. Ships and sub's can interdict supplies, production and troop transfers. I've been pretty free in my ability to move stuff around without much hinderance.
Anyway, I'm NOT trying to be overly critical. Sorry, if my post comes off that way....but I think if you try to employ some of these tactics with the PDRC... you'll see they are alot more competitive power.