If you look at the Soviet Navy the Frigates were the Krivaks which generally had half the main missile fire power of the Destroyers... four large missiles for Krivak compared with 8 for Sovremmeny and Udaloy... so essentially it was a big corvette with better endurance and better guns.
Krivak with 3500 tons a corvette ??? what is a "big corvette" ??
an then, a Buyan-M with 900 t., what is that ?? a rowboat ?
Well, I am amused by the modern classification of ships that they want to impose.
In my country, Aegis 6200-ton anti-aircraft destroyer is called a "frigate" so as not to appear aggressive.
The corvette was a small and light ship with less than 20 guns, the frigate between 20 and 60, and the ship of the line more than 60.
There were ships of the line with two bridges 60 to about 90 and three bridges about 90-120. (In my country "Santisima Trinidad" had 4 bridges and 140 guns, was sunk in Trafalgar in 1805)
In modern times the corvette was a coastal vessel of between 500 and 1500 as a very, very high limit.
The frigate was a 1500 to 2500 or few more as much, escort ship with anti-submarine orientation. In WWII they were called Escort Destroyer "DE"
The destroyers were more than 3000t. and with a much higher speed and armament (30-35 knots)
Of course, all of these classifications change with changes in shipbuilding.
However, there is a way of classifying that does not change, which is that of the officers who command these boats.
The ships are divided into three ranks:
Corvettes are 3rd rank ships. His captain is a third rank Navy Captain, in the USA I think he is called "Lieutenant Commander", in my country he is simply called "Corvette Captain"
Frigates are 2nd rank ships, their captain is a second rank Navy captain. In the USA it is "Comander", in my country it is simply "Frigate Captain", equivalent to Lieutenant Colonel
The Destroyers and superiors are 1st rank ships, their captain is a first rank Navy captain, in the USA he is simply called "Captain", in my country "Captain of Navio" (Ship of the Line), equivalent to the rank of Colonel.
So what is the classification that Russia gives to the «Steregushchiy» class according to its military potential ????
https://ru.wikipedia.org/wiki/%D0%9A%D0%BE%D1%80%D0%B2%D0%B5%D1%82%D1%8B_%D0%BF%D1%80%D0%BE%D0%B5%D0%BA%D1%82%D0%B0_20380the project 20380 (20385) of the «Steregushchiy» type are ..... patrol ships of the 2nd rank with guided missile weapons for the near and far sea zones...
Of course with 2250 tons, 27 knots, her armament and her mission, she is a 2nd rank ship, therefore she is a frigate, as is logical and normal. Her captain is a Frigate Captain ("Commander" or NATO OF-4)
I think these ships come to fill the gap left by the Krivak with their premature retreat, therefore it is the normal gap for the Frigates.
Besides that, the "Frigates" of the 22350 class are classified as 1st rank ships, therefore with their 5400 tons almost 30 knots and their armament, Russia actually considers them destroyers.
And from what it seems, they come to fill the gap with the premature withdrawal of the Sovremennyy destroyers, of which only 3 of about 17 remain, and even so, they hardly sail.