I think we can agree that it's more then a redesigned Flanker. The basic aero-dynamic layout may have been retained, but the airframe is different, all the avionics are new (and the radar in question isn't an upgrade of the previous one) the OLS is new, and even the engines (for all the discussion currently) are going to be different.
Let me put it this way. If the JSF program, to raise funds lets say, used late-model F-16s as testbeds for some of it's sensor, and engine, improvements; would you consider the JSF a continuation of the F-16? I mean the basic aero-dynamic layout is not THAT different.
Lets say we retrofitted EO-DAS to an F-16 airframe, along with a radar that will later evolve into the F-35 radar, and a new engine, that will serve as the baseline for the F-35 engine.
I mean ultimately, there's only so much money Sukhoi has to play with. And the MoD funding for the PAK-FA was poor, and came late. So of course they had to cut corners, and extend some of the upgrades to late-model Flankers to help pay for the PAK-FA. From what I recall even some of the RAM coating used on the Su-35 may go into the PAK-FA.