Well their aircraft is more or less an Indian designed KF-21... with internal bay, same engine, same size. Would be just clever to go with them at this rate, KF-21 will have internal bay in the future...
They claim VLO. That's a whole can of worms KF-21 hasn't yet touched, without which they're at most members of the happy <1m class.
Yes, it'll help to actually have that 1m, and not "1m*
*before stores". It isn't that much of a gain for a purpose-designed 2030 aircraft; normal detection ranges against 1m RCS can now handily exceed normal combat ranges, and not like moderate stores add
that much RCS. You won't be getting a magic advantage over Eurocanards by just removing weapons inside, and J-10 will still detect you. MAWS feels itchy.
Bay itself at the same time comes with a significant increase in volume/wet area (significantly worse performance, you effectively add as much volume as would otherwise move you to a higher aircraft class... especially with serpentine intakes), and adds very delicate bay release trials you'll have to repeat over and over. Especially supersonic/high AoA ones. ($$$)
But if we want more.
Flattening/replacing/neutering all protruding antennas, flight sensors, edge treatment structures, treating access hatches (in a way that allows actual access), and all secondary intakes, fully treating primary intakes and engine fans even behind s-ducts.
Getting to magic .1 sq m RCS (which, btw, isn't F-35/J-35 and J-20/F-22 level, it's"just" Su-57) is a whole industrial enterprise, reinventing half of the plane. You can see lots of small pieces of this job now actually done by Turks.
KF-21, right now, is far from even "cheap stealth" (aka, geometry only).
Adding a second zero to your RCS figure (to notional 0.02-0.05) requires further treatments and sacrifices, as you combat physical phenomena that were negligible, but now form a big chunk of the signature.
To be fair, Koreans even explained specifically that it is currently not VLO, only that a future version (a different aircraft in all but name), potentially, can be. It deserves credit and respect.
At the same time, they wasted
a lot of performance on this claim; KF-21 replaces F-5, and as such, the ROKAF requirements to it were really low. Still, they got ~KF-16 level practical performance on a substantially larger aircraft with 2 engines, and Korea will be paying for that. But, this was a conscious sacrifice.
Heck, even Gripen E can cover the same mission set KF-21 does, on literally
half of its power and fuel.
In the Indian case, the most experienced manufacturer in the country (HAL) struggles to get out of production hell without all these complications.
