Your biggest failing is you are paper focused...
Just because something is bigger or more powerful does not make it the natural choice or replacement option.
A carbine rifle is much more accurate and powerful than any pistol... for a front line police officer however a pistol is vastly more convenient to carry and use even if it has terrible range and power in comparison.
It does not matter that the 120mm calibre is more powerful and has better range than an 82mm weapon.
Just the same as with the ZU-23 towed weapon discussion we had... sometimes the on paper better self propelled model seems an obvious replacement option it ignores other factors... including cost and mobility.
The 120mm calibre system is of course going to be a useful replacement for the NONA system, but that does not mean a lighter 82mm system on a smaller lighter vehicle is out of the question.
You are correct when you say not everything developed is accepted into service, but they don't just develop things at random... there are specific requirements for each design and not all of them are satisfied simply by putting a slightly bigger gun on it.
The 30mm cannon is potentially replaceable in many roles because it has become obsolete in many roles...
In the IFV role against armour is it obsolete because potential enemy IFVS are not really vulnerable to 30mm armour piercing rounds any more.
In the AA role the 30mm is still effective against manned aircraft but not so effective against small UAVs.
Air burst rounds would improve their performance against such targets but the 57mm calibre rounds will be rather more effective because of their heavier payload and the fact that some of their rounds will be guided.
That does not mean the 30mm is obsolete for the APC role (as seen on the BTR-80A type vehicles now), but in that role it is mostly used to deliver HE payloads to targets... a 40mm or 57mm grenade launcher or a 23mm cannon using the lighter medium velocity 23 x 115mm rounds would be much cheaper and hold more ready to use rounds... much less recoil and smaller lighter systems.
With modern FCS it should be just as accurate if not more so because of the low recoil and high rate of fire.
And no, there is not a reason to avoid the use of armoured vehicles and aircrafts because of the existance of MANPATS and MANPADS. Today, with the apparition of Rocket Assisted Projectiles, all the armoured vehicles and aircrafts present in the Russian Armed Forces can be able to work from outside the range of the man portable weapons of the adversary, unlike the 2S41 that never will be able to do the same.
In a modern combat situation unless you are operating in a totally flat desert will have plenty of scope for dead ground... ie places to hide where from the targets perspective you are not visible.
Lock on after launch weapons will be able to be fired from behind cover so you will never see the platform that fired the weapon.
To turn it around and talk about Russian systems the laser target marker on the MiG-35 has a range of 20km against ground targets... a radio call to ground forces and a mortar team less than 2km from an Abrams could fire a single laser guided mortar bomb at it and the Abrams crew might have a small hill between them and the mortar team, yet the MiG-35 can detect that Abrams and pass on its coordinates to that mortar team... they know their own position and can calculate the angle and elevation they need to get their round within 500m of the target... they can fire one round and then move. The MiG-35 pilot will get a signal when they fire their round and 4 seconds before impact the Avionics of the MiG will automatically lase the target for the next 5 seconds... the nose cap of the mortar bomb falls off as it starts to fall towards the target Abrams... 3 seconds before impact it will see the laser beam on the roof of the Abrams and it will manouver to hit the top of that Abrams and boom.
Are you telling me the only way to protect VDV vehicles is to armour them like Abrams and fit them with guns that fire to more than 10km?
Even in a city you could put that mortar team two streets away and all the buildings will block the view of your crew... even without the laser guidance a mortar can shower rounds on targets less than 500m away without being able to actually see them.
Missiles like Javelin are fire and forget and it is known the Russians are working on something similar... but I rather suspect much cheaper... so that they become more practical.
A diving top attack weapon will kill anything no matter what sort of armour you have or what range it was fired from...