The original Su-27 design was designed from the outset to have a certain percentage superiority to the F-15 in various aspects... (this is quite normal... the F-16 was designed to be something like 30% better than the MiG-21 in manouvering aspects (not speed))
When they built the first flying prototype of the T-10 they found it was not superior to the F-15 base design at all, in fact it was inferior... so they totally redesigned it... which took time and money.
Right now the An-26 is getting close to its expiry date, so time is running out... their best bet would probably be to sort out the current design issues and then start on the improved Il-112VM design with improved specs.
I mean this thread alone started in 2010...
According to the posted figures the difference in max weight for both aircraft is less than 2 tons yet the slightly heavier one has much better range with a much better payload with less powerful engines.
Just looking at the prototype the Il-112V seems to be mostly made of composites (yellow) with only specific parts made of aluminium (painted white) where strength is needed like control surfaces, plus obviously the dielectric panels for the nose radar and other sensors fitted.
Would be interesting to see empty weight figures for the Il-112V and a comparison of fuel burn rate stats for the engines of both aircraft...
Of course if it can exceed the performance of the An-26 then it will already be an improvement, but working out the difference might be useful for further development of the aircraft.