Yes, THOUGH one might define a modern Flower corvette as an escort that usually or mostly keeps the escorted convoy alive (if at least two escorts are present), NOT as a threat platform killer.
Keeping alive can be done by alerting the convoy in time about a probable submarine contact so said contact can be avoided (run away from) and possibly be dealt with by a MPA.
Add CAPTAS-2 or even only CAPTAS-1 (though that may be optimistic) and multicopters for delivery of LWT (preferably the most lightweight models) and more importantly of sonobuoys (mostly to weed out false contacts) and you should be fine.
If your corvette is escorting the convoy, then its sensors aren't actually involved in the hunt for the enemy submarine. The Northern Fleet only has about a dozen SSNs and SSGNs, and it would need most of those for bastion defense of its own SSBNs. Against a half dozen enemy submarines, a barrier patrol on the GIUK gap using aircraft and SURTASS ships is far more efficient than close protection of merchant shipping.
LWTs from surface ships are useless against modern submarines when the submarine can hear a container ship from 100 miles away. There's no reason to pretend that could be an effective tool for self-defense unless you use the LWTs to destroy incoming HWTs. Without a Mk 41 VLS for VL-ASROC or something larger like the Sea Lance, the only way to use them effectively is an offboard launch platform, which could be an ASW helicopter, a UAV (minimum size is likely to be something like the MQ-8 Fire Scout), or a USV carrying the torpedoes.
Moreover, one might consider the ability to fend off a salvo of up to 40 AShMs with two such escorts as necessary regardless of how close a hostile sub may come. Sub-launched AShMs outrange even CAPTAS-4 and equivalent missiles could even be dropped from airliners.
Defence against said AShMs might - in absence of AEW - happen at no more than radio horizon distance. There's no point in having some 300 km range radar and 150 km range missile against 30k ft altitude targets when threat missiles would approach at 5-10 m and become visible at horizon only. So horizon range against threat missiles at 5-10 m, about double that against higher-flying supersonic missiles. A rotating Thales NS50 (a rotating radar for lower cost) and gimballed optronics sensor coupled with IRIS-T SLMs (relatively cheap horizon-ranged SAM with supposedly good ceiling) and lots and lots of decoy launchers (including containerised on the escorted ships) should work fine.
I don't think a salvo of 40 AShMs is realistic against a civilian convoy. Simply not a good use of a high-value SSGN's capability and expensive missile load... (Against a carrier task force certainly, but that's already a very well defended target)
A typical convoy with 2 corvette escorts (one each side) might be 15-18 ships (3 columns of 5-6). Even if each corvette had only a simple defensive SAM system with 8-12 ready-to-fire missiles (as small as Mistral or IRIS-T SLS/AIM-9X) that should be enough to deal with decent-sized salvos and significantly limit the attacker's ability to dent the convoy.
I wouldn't be worried about a huge number of Oniks missiles. Using a Tsirkon or two from long range (100 - 200 miles) against the frigates (or corvettes) before closing to engage the cargo ships with torpedoes would be more efficient, and very few European frigates would have any defense against a quasi-ballistic missile. Unless you deploy AAW frigates and destroyers with every ASW group, then dispersing systems like ASW helicopters is going to preserve more capability during an attack.
Another problem with close escort is the speed. Container ships can sustain 20 - 25 knots, and the only ships both faster than that and large enough to carry helicopters are purpose-built warships (unless the convoy escort is a container ship converted like Atlantic Conveyor). Dropping that requirement by not escorting convoys gives you a lot more flexibility in designing and operating smaller ships and USVs for the ASW role.
So…you think a submarine is going to 100% give away its position to launch a missile at a cheap low end ship, so it can then be engaged by helicopters from other larger ships that maybe nearby, or land based MPAs?
If a submarine and an ASW asset run into each other, it's because one of them knows the other is there. Do you think a submarine attacking a convoy would just not bother engaging the escorts? If so, then there's no reason for the escorts because apparently they can't do anything. If it's not an escort scenario, then the appearance of a sonar-equipped enemy combatant means that the enemy already knows where the submarine generally is, so shooting the first enemy sonar as soon as possible will give the submarine the best odds of breaking contact and escaping before other assets show up. That being said, the first asset to respond to cueing from something like SURTASS is going to be an aircraft or helicopter, so the submarine will already be sunk or escaped by the time any surface ship shows up.
