Wrong! Adding a digital internal nav sensor fused into a modern weapon system backed by a phased array SAR radar increases the Kowsar's real world capabilities far beyond anything standard F-5E could even dream of so despite the fact that it's same platform in terms of actual capabilities that matter the differences are like night and day so all the bells and whistles you speak of most definitely matter.
And you like mentioning the fact that the platform is a 60's era platform as if the F-15, Su-30's,.... were designed yesterday! F-15's are also a 70's era platform and yet today they remain one of the deadliest fighters in the sky's all because of all the bells and whistles that were later added.
As for the Yak-130 it would be absurd for Iran to chose that Aircraft over the Kosar especially after the very hard lessons Iran learned during the Iran-Iraq war. Especially with the Kowsar Iran now has a domestic platform that it can design various PGM's around based on our own needs and specs and that is far more valuable to Iran than any imported fighter let alone a low end CAS fighter like the Yak-130.
As for the range of the radar the F-5E's radars had a Max range of ~40km where as the Kowsar new radars at the very least have a range of 150km and F-5's or Kowsar's are CAS fighters that will mainly be operating within ~250km of their home base so they will be fed target data from the ground for better situational awareness and that will more than make up for their lack of range (comparatively) so depending on the weapons they will be carrying ~100km targeting capability would be more than sufficient to hold their own over Iranian airspace. And actually the main problems Kowsar radars will be facing compared to an AESA equipped fighter is NOT range but rather speed of detection. Today it's a matter of how fast you can go radar on, search, detect, lock, fire & hit and go radar off again... And that is again another vital upgrade Iran will have to address....