Ganzo has certainly copied other designers in the past. This has invited a lot of hate on the forum and I think it causes some people to overlook anything good they do. For instance, Ganzo does have original designs (or at least designs which don't infringe upon the intellectual property rights of American companies). The quality on some of these designs is excellent for the price. Take a look at their FH series. I have the FH11. Compared to other sub-$30 knives, it is very impressive. The action is on bearings and is quite smooth. The lock-up is solid with no blade play. It came sharp and cuts well. The D2 may be "foreign" but it is real D2, it is treated to a hardness of 62 HRC, and it does hold an edge better than lots of knives I've owned in 8Cr13Mov or AUS-8.
D2 it is a tool steel that can be made very hard. This is good for edge retention. However, it tends to be more difficult to sharpen. It also has less corrosion resistance than many stainless steels. The difference between "foreign" or "imported" D2 isn't the steel but how it is treated by the companies using it. Higher end companies will take greater time and care in heat-treating and tempering steel. Of course, this is typically reflected in the cost of the knife. Given the complexities involved, it shouldn't be a big surprise that the D2 blade on a $25 Ganzo doesn't perform as well as D2 blades on knives that cost two, three, four (etc.) times as much. That's not really a fair comparison in the first place.
Here are the results of D2 cutting performance from that recent "SuperSteel Steve" test correlated with current Amazon prices. Notice that the Ganzo FH11 did outperform the Steel Will Cutjack. Also note the strangely large difference between coated and non-coated blades for the Rat 2.
Knife - Fine Edge (rounded feet of cardboard cut) - Working Edge (same) - Cost (rounded US Dollars)
Rat 2 (Coated) - 104 - 127 - $41
Rat 2 (Satin) - 86 - 118 - $37
Cutjack - 73 - 102 - $38
Ganzo FH11 - 77 - 113 - $26
To make a long story short, D2 has some good qualities but it isn't necessarily the best steel for a budget knife. Like any steel, a lot depends on what the maker does with it. I generally prefer stainless steel for EDC. I like 14C28N. I've recently had good experiences with 9Cr18Mov from Civivi and Acuto 440 from Tangram. I think Civivi and Tangram are great places to start if you're looking for a great budget knife.