Iran has a number of F-5E to phase out. The only realistic replacement is JF-17 Block 3. Even if Trump loses election and the US gets rid of sanction on Iran, the fact that Gripen and Tejas both use F404 makes them unreliable for Iran. JF-17 Block 3 is the only other plane in the light fighter category. JF-17 block 3 is the only realistic option for replacing F-5E in Iran.
You logic makes sense but it's just an educated guess. Consider several other things.
1) Iran got the fighers it has as an inheritance from a previous regime, not a set of procurement decisions. It's not clear that the F-5 replacement has to be a light fighter or has to be 1 for 1.
2) Iran likely can't afford to replace it's entire fighter fleet. Older aircraft will continue to serve for quite some time, so the decision may be less about replacing what they have and more about adding what they don't have.
3) Iran has limited funds and the Su-30SM is relatively cheap. Note all of Russia's cash-strapped partners went for it, Kazakhstan, Belarus, Armenia. (in point of fact Kazakhstan isn't doing too bad but their defense spending is limited, it's not the country but the military that's relatively cash strapped) This could be the deciding factor. Note, Myanmar also purchased the Su-30SME.
4) Iran has already shown interest in the Su-30SM, and I suspect the Su-30SME variant was aimed in part at Iran. Russia's CSTO partners get the domestic SM variant, and others get the regular MK export in whatever their chosen variation is. The only exception is the above-mentioned Myanmar, another isolated regime that wants relatively sophisticated weapons at an affordable price.
Note, it's entirely possible (likely even, in my opinion) that Iran will get the JF-17 in some version. But with presently available information I don't think we can confidently state that they will get a specific version for a specific purpose. Though if you have evidence to suggest that the Iranian military is thinking about it in those terms, please share.