Well, this topic has been dead for quite a while, but hey, I just found it.
To answer the original post, no, there is nothing wrong or inferior with the design of the E body suspension system. It is, as other already responded, actually a very good design. What is usually the biggest trip ups for people comparing their vintage mopar to a modern car is limited to only a few of things; spring rates, alignment setting, and road feedback. improving these three things can usually provide huge dividends on the perception of handling. Also don't forget that these are 30+ year old cars. A lot of perception can be changed by simply firming up the chassis. Sub frame connectors or torque boxes should be the first thing anyone should do if they intend on doing anything more than driving to the local show and shine.
First and foremost are wheels and tires. Modern radials with light weight wheels provide big increases in gripping power. 15s are fine, but 17 inch wheels have the bigest selection of tire choices for performance driving and are popular enough that they can be found with 40, 45, and 50 aspect ratios to keep your muscle car from looking like a honda. You just have to look at the SUV tires instead of car tires.
Springs rates are typically 15-25% higher in a modern car than they were 35 years ago. For street applications, I really like the .96 bars for small blocks and 1.0 for big block cars. In the rear use the stock style XHD spring pack which is around 140# rate. Sway bars should be at least 1" front although 1.125 is better. Firm Feel offers a 1.25 if you really want to tame corners. Match this with a .875 or 1" rear bar and your cornering flat. To companion with the springs, get as good a shock as your willing to spend for. Edelbrock IAS are a good starting point, but bilstein, carrera, or koni are the best choices. Parts store units and KYB just aren't up to controlling these increased spring rates in a comfortable way.
Most alignment shops, even if they know how to work on a mopar, will likely use the vintage 1970 specs which were designed for skinny, bias ply tires. Radials can take a much larger range of alignment changes, which will provide HUGE changes in feel and is where a lot of the modern difference lies. Before you take your car to the shop, make sure you have the wheels and tires you want on it, engine and trans in, etc. and set the ride height where you want it first. If you riase or lower your car after alignment, your settings over every other spec will be off so do this first. Once that is done, tell the shop to leave it as it sits and ask for these settings; Caster, as much as you can get. Usually 4 degrees is the most you'll find without getting into parts replacements, but if you can get 5 or 6, take it. Camber, -1/2 to -1 1/2 degrees. The more you actually are driving the car in corners, the higher you would want this value to be. -1/2 is probably fine for you if your just tooling around. Radials can use this -1/2 without showing significant wear differences and hte change in handling is large. Toe should be set to 0 and no more than 1/16 in. Again, if you actually use your car for road course you may want to go with 1/16 toe out, but on the street this makes things feel very "darty" so you don't necessarily want that.
The stock mopar steering has always been over-assisted. The only way to solve this is to replace the steering box with a firm feel unit or a manual box. The increase in road feel provided by these allows you to know how you car is responding much easier. There are also the fast ratio pitman and idlers which are nice, but at high speeds,100+, are actually too fast. Cup cars and land speed racers typically use a much slower steering rate than street cars.
These are all relatively easy, bolt on type changes. Obviosuly if you really want to get serious you need to look at increases in chassis stiffening, changes to poly or delrin bushings, bump steer corrections and more. Something not mentioned above that takes considerable work but also pays big dividends is gusseting the stock steering box mount. Next time you car is idling in the driveway, have a friend jump in your car and turn the wheel. You'll be amazed how much the steering box moves around in there.