Putting the Analog-Digital conversion function so close to the antenna input of the receiver allows the receiver designer to either optimize or cut all corners in the cost versus performance tradeoff even more than the traditional superhet designer ever could.
And so there have been, and will continue to be, well-designed and robust SDR receivers (expensive) along with corner-cutting SDR receivers (not expensive), just as there were good and bad Superhets. The RTL dongle is an example of an all-out corner cutting (most inexpensive) SDR. Sherwood shows us what the most optimized (and expensive) designs can achieve. All other SDRs are somewhere in between those two examples.
Meanwhile Analog-Digital Converter sampling speed, sampling clock quality (stability, phase noise), noise floor, DSP noise reduction algorithms, and so on can make huge differences in performance. That's on top of the traditional things like audio chain cleanliness, power supply noise immunity, front panel control and cabinet design and robustness, transmitter audio and RF signal quality, antenna tuner insertion losses in high SWR conditions (which they almost never admit to you), and instruction manual usefulness.
Product and warranty support probably adds 5-10% to the cost of of a radio, depending on how well the radio is designed in the first place (I base that estimate on what my employer's allowance for warranty repairs and support is). The rest of the cost is determined by how many corners the designers chose (or were told) to cut. There will be no such thing as a world-leading performance SDR from anywhere that is miraculously half of the cost of all the others, unless the manufacturer is dumping them into your market. It would become very apparent after the new owner takes off their rose-colored glasses (or headphones).
Product reviews that give 5 stars in spite of lack of product support, lack of a useable manual, lack of normal robustness controls and buttons, and/or lack of reasonable quality connectors, but because the price is low, they can throw it away after a year, just annoy me.
73, Ed