Radar has long been Russia´s weakness in jets. They were very late with the shift to AESA from PESA. And India has long complained about poor maintenance and service quality. Indeed, Israel earned itself a lot of money because they have many ex-USSR engineers who worked in the defence industry prior to emigrating to Israel and know the ins and outs of many Russian MIC products. That was at least the case in the early 2010s. Maybe things have changed now as many of those guys have retired.
This lateness is schedule based. The only serious "culprit" when Russians were late to actually propose AESA is Mig-35, where phazotron tried for MMRCA, but couldn't demonstrate workable AESA.
All major 2nd gen Russian flankers went into volume production around late 2000s(~2010), having PESAs. Which overall didn't terribly matter, as both Bars and Irbis still produce reasonable performance for the class. Furthermore, it isn't like in 2000s AESA was everywhere - only americans produced early(not really superior) AN/APG-63v3 for 4th gen at some scale...better not mention Japan, as until 2010s their beautiful AESA had like 40km detection range v incoming aerial target (i.e. simplest scenario). French RBE2 (which is also a very modest frontend upgrade) came later. AN/APG 79(Super hornet) and 82(strike eagle) are more of the same, but with better multirole (still old, 1990s) backends. Chinese AESA comes later still - around mid-2010s.
PESA only truly can't match AESA performance when there's new backend and integrated architecture(allowing MESA, aka multirole functionality beyond just radar); otherwise it's somewhat secondary; what trully matters is electronic scan and revisit(in fact, you can make LPI PESA...again, with more capable backend, of course). Yes, even frontend AESA produces better(sharper) directional diagram, it's more resilent - but it's also lower power, all things equal, and damn thick(no easy 3d mechanical scan).
As such, Su-3x were procured with whatever was available (to be exact - su-30mki/sm - whatever available, su-34 - inherited ground attack radar from cancelled bomber, su-35s was designed specifically as a platform for its radar set). It was quite alright for the moment(by large, it still remains so - PESAs are significantly more useful in modern environment when compared to world average - which is planar PD arrays). And for a decade after that, they didn't need upgrade.
Russian AESA became available for series produciton(not as a prototype) around 2015, beginning with Su-57. But since first batch of T-50 failed trials, it had to "wait" that aircraft reaching production.
By comparison, J-10C and J-16 went into production more or less around same time; as such, their schedules aligned with AESA development, and were launched into production together with their AESA sets.
Now, as 2010s flankers reach MLU update stage, they're in line to get AESAs, too. Su-30SM is first, its just a lower hrs airframe, and it's as MKI is by far the oldest of 3. NIIP proposed Indiands to update their MKIs to AESA since late 2010s, and now it's what happens with Su-30SM2. What happens with Su-34 is a mistery, because its radar is an orphan(soviet research institute developing it collapsed in 2000s). Su-35s's Irbis upgrade is also an enigma - it's impossible to fit modern pre-SiC AESA on that swivel, it's just too thick and heavy.
But su-35 is the one with least need for upgrade in the first place.
Whatever the case, back to Indians.
So India had option to fully update their MKI(which are, a reminder, still 2002 standard by large) around late 2010s. This included AESA, RVV-SD, R-37M, and so on. Indians are, of course, smarter than getting "just" a GaAs frontend (and corresponding weapons, when there's the mighty Astra mk.5...where is mk.1 btw), and want full new GaN radar; this was, of course, only for Sukhoi, because ELTA-2052 installed in Tejas mk.1A and Jaguar is exactly a frontend GaAs upgrade with added weapon package included(Derby). This ideal Indian AESA will optimistically come around 2030(i.e. again likely later than Russian GaN). And while Indians wait and discuss their ideal solutions, they fought two big border skirmishes(2019, 2025) - both with early 1990s A-A weapons (RVV-AE in Balakot, RVV-AE and MICA-EM in SIndoor).
Given this tempo of border accidents - they'll probably fight a yet another one, in more or less same ~2000 level capability of their fighter fleet. Which is entirely Russian fault - totally not Indians somehow deciding to buy RVV-SD(aka r-77-1 export) only in may 2025,
after Sindoor. And, of course, their beautiful Rafales were ordered with mid-1990s MICAs, too... because France doesn't even have anything better yet, and while RBE2 is indeed an earlier(2012) AESA - it is sensor, not effector: by itself it can only angrily radiate target, hoping for eventual painful cancer.
But since it's (uh)French, pointing that selling fighter aircraft with museum weapon outranged by a factor of 2...3 around 2020s is inappropriate. And who the h even knows where those meteors were.
