Soviet and Russian technology in ballistic missiles is world leading. The Iskander is a limitation they agreed to due to INF treaty. They already had the long range Oka system before the Iskander and were forced to scrap it.
Yavar once pointed out here or on IMF that compared to the Fateh series, Iskanders for Russian service have thrusters for exoatmospheric maneuvering. I wasn't aware of that back then.
Fateh series lack this feature.
Iskander is believed to have Hormoz-1, -2 and Fathe Mobin like seeker options. It also has submunitions and FAE warheads as far as known.
Flat, quasi-ballistic trajectory is a feature both are expected to employ.
So Iran is getting there.
Another question could be which weapon is more cost effective and here the Fateh family could have the upper hand.
Could the Dezful at its max. range employ a more accurate INS? Well possible.
But otherwise, just imagine a Iskander / 30 years old Oka hybrid. Soviets were that far when Iran just had got first SCUDs.
Which one is better? Of course the Iskander can easily be upgraded to Dezful-like range. Because the Dezful looks like the more cost effective design, is more recent and has a separating RV that makes it a smaller target... I would say Dezful is at least a contender to the masters in this field.