Shields on UNSC vessels, ability based or not, are absolutely not happening, period, no discussion. Covenant defenses,, and specifically the patrol station, can very much be dealt with by the UNSC through a number of methods, from un-counterable cloaked Saharas, to Artemis classes doing a shoot and scoot, to "sacrificial lamb" fleets to absorb the brunt of a Patrol Station fleet or even kill the station beforehand, to other methods players have developed over time. Further, the UNSC has a number of play styles that the Covenant cannot replicate or pull off as effectively, such as any style that uses attrition warfare, any style that makes use of irregular warfare/sabotage (Sahara), and defensive/turtling combat (SMAC network/Anchor is superior to Patrol Station/CDA).
The claim that plasma torpedoes are "just as strong (near as makes no difference) to the MAC" does in fact give some credence to this statement, as this absolutely false when comparing UNSC and Covenant ships of equivalent cost and role. A great example of this is the SDV versus the Halberd. The SDV does 625 damage per shot while the Halberd does 1800 damage per shot, with their respective primary weapons. In other words, the UNSC has extremely high alpha damage, which allows them to wipe out large chunks of an enemy fleet before they can bring their firepower to bare, or important in the case of the Covenant, kill ships before they have a chance to make use of passive health regeneration (ex. shield restoration). Further, unlike the Covenant whose ships all have variable cooldowns, the UNSC MACs, on all ships save the Infinity, all have a cooldown of 60 or 70 seconds, allowing for coordination between volleys.
I would highly recommend looking into all of the tools at the UNSC's disposal as it seems evident that they are not all being used to their full potential which is leading to the thought that the UNSC is underpowered, when that could not be any further from the truth.