125mm dia restriction.
The present Konkurs is 135mm right. So if that fits, why a specific requirement of downsizing?
Anyways my only real concern is the range. MP ATGM, or Amogh 3 or VEM technology 3rd Gen ATGM , all won't be able to complete the requirements. Javelin & Spike are having bigger diameters , so would be difficult for them too.
125mm means it kicks out all existing ATGMs forcing OEMs to develop new ones. It helps DRDO, MPATGM is 120mm.
Range is less of a concern. The Ukraine war's shown more range is useless, tanks are simply driving away in the time it takes. And direct attack has been more successful than top attack. Plus it appears new armour tech and more and better ERA placement have defeated existing ATGMs, so the Javelin has been failing consistently.
Here's a tank crew escaping two shots.
The only reason this tank got hit the second time was because of its sh!tty reverse speed common to Soviet era tanks.
The Russians are also using the weather against the Javelin, where dusk and dawn temps are similar to the tank's treated temp. Thermal crossover is lowering accuracy.
With the exception of some sporadic successes, particularly against weaker armour like IFVs and older tanks alongside quite a bit of incompetence, the Javelin isn't that crucial anymore. So a new missile is necessary.