They are place holders (upgraded older ships), they don't need to be super overloaded with missiles... just cheap and simple and represent Russia anywhere on the globe.
I would expect the new Frigates and Corvettes will be used near Russian waters, though they might be sent on longer trips like pirate chasing off the coast of africa with a support ship to give it the endurance to remain longer periods than its size would normally allow.
Sending a Corvette for two weeks operations makes no sense if it takes two weeks to get there, so having an endurance of a month... two weeks to get there leaving two weeks on station and then two weeks to get home it is not very efficient... sending a frigate will still take two weeks to get there and get back but it might have a two month endurance, so it might spend 4-5 weeks on station and then two weeks back.
These upgraded destroyers are called frigates to reflect their armament... which is no good for taking on all of HATO but for use against pirates all it needs is a big gun to sink small boats, deck mounted HMGs and hand held RPGs, and of course a helicopter and a group of naval infantry to board and capture boats... plus some high speed inflatables too.
Its much bigger size means more space for stores and its improved tech means more free space and perhaps a smaller crew for normal operations, so it might be able to operate off the coast of Africa for 2-3 months, and with support ships bringing supplies and maybe crew for crew rotations they could stay there without constantly making trips back to Russia... but that all applies to other locations too... longer time on station is very important and that comes from onboard storage space... which comes from the opposite of filling every nook and cranny with missile launch tubes.
we over simplify outside looking in.
Indeed... it is very easy to evaluate a ship by the number of missile launch tubes it has, but if that is all it has then you might find it is not very popular amongst its crews.
For the Cruisers and the Destroyers it is certainly an opportunity to try larger propulsion alternatives and larger calibre guns and larger sensor arrays (sonar and radar and optical systems), but ultimately they will hopefully be replaced by new build models.
The older ships upgraded fill a gap, but also offer an opportunity to test new stuff that will be put on the new destroyers and cruisers they end up making further down the road.
For those thinking they don't need cruisers, a cruiser is not just a bigger destroyer, it is a class of ship that is designed to manage operations from and to organise the collective defence of a group of ships or an area of sea.
A cruiser is big enough to carry enough surface to air weaponry to not just defend itself, but to defend other ships around it... it is the sort of ship that is critical if you have lots of other large ships that can't have an enormous air defence capability.... like helicopter landing ships and aircraft carriers as well as all your support ships.
If you think of it in air defence terms a corvette is an SA-15 system or a Pantsir system, a frigate is a BUK, or an S-350 system plus a Pantsir or TOR, while a destroyer is an S-300V and S-400 system plus Pantsir or TOR and BUK and S-350.
A cruiser adds S-500 and Nudol and everything else as well, and makes it possible to also have an airfield with Su-57s and a pint sized A-100... but it is not just adding these missile systems it also adds much bigger and much more powerful radars and sonar equipment, and it also carries all those missiles in much greater volumes than the smaller ships can carry.