How can you say it looks like the J-10 can beat it aerodynamically...? We don't even have a proper picture of it yet, and the shots of the F-60 models were at strange angles so we cannot tell its real proportions.
As for stealth shaping -- how does the DSI look dubious, it looks fine to me (going by the model). I agree the trailing edge of the wings at this point do not seem to be the standard trapezoidal shape present on stealth fighters, but SAC are not that stupid to not align the edges on a plane together. (dependign on which picture you look at. For instance in this pic of F-60 you can clearly see the edges of the wing and stabilizers are aligned once you compensate for the latter's slight difference in elevation)
The aircraft has been estimated to be in the size class of F-35, which is not that small at all.
I won't say this is meant to be a cheap stealth fighter, but certainly a more affordable, probably more multirole airplane than J-20's air superiority role. It should be able to carry a payload of four MRAAM size weapons at the minimum, and will obviously suffer a shorter range than say J-20, simply because of its size. But those are things every medium weight stealth fighter under development will suffer (F-35, ATD-X, KAI KFX, AMCA).
At this point I see nothing to majorly dislike about J-21/F-60, if it looks like what the model shows. It's basically a twin engined F-35. It gives opportunity to be modified for carrier operations too, given its configuration (say compared to J-20), and the two engines will definitely be a benefit in that regard.
