The problem with comparing the Rapier II to the Hellcat is that we don't know what their stats are for CONTEMPORARY versions of the fighters. We don't know what the stats of the Hellcat V would have been in the WC2 timeperiod, and we don't know what the stats of the Rapier II would have been upgraded in the WC3 time period.
The F-16 Falcon and the F-18 Hornet were designed at the same time, and initially the F-16 was the superior design (20-30 years ago or so) and was put into production in larger numbers. However, as technology has evolved, the F-18 has proved to be the better fighter when upgraded with 1990's and 2000's technology, and now is much more heavily employed.
I always thought of the Rapier II and the Hellcat in similar terms. Maybe they were designed at the same time (the similarities in their hull shape and wing layout always suggested this to me), or maybe the Hellcat really is older, and in the WC2 era, the Rapier II was the superior design. As component technologies were upgraded and improved on, maybe some of these upgrades degraded the Rapier's performance more than the Hellcat's, and so by the time WC3 happens the Hellcat V versions that appear then are superior to how the Rapier II's would perform when upgraded with similar technologies.
For some purely conjectural examples of how this could occur, maybe there was some advance in reactor technology that extended the range of the fighters, or improved their reliability, or eased maintenance, or had some advantage that all fighters needed that upgrade in order to stay competitive. Maybe the new reactor was slightly more massive, or bulkier, and the Rapier's chassis couldn't support that upgrade, while the Hellcat's could, or maybe they both could support the upgrade but various engineering shortcuts in the Rapier's design meant that it's max speed dropped by 300 kps whereas the Hellcat's dropped by only like 50 or something. Or maybe the decoy system that is standard in WC3 but almost non-existent in WC2 simply couldn't be mounted on a Rapier II whereas it could on a Hellcat V. Or maybe some advance in gun technologies necessitated a differently designed shield generator to counter, and that generator was not compatible with the Rapier's design, or if it was, could only produce shields so weak that the Rapier would be inferior to the Arror.
Or maybe it is just a simple matter of the designs being roughly equal, and we happen to be on ships with Rapiers in wC2 and with Hellcats in WC3.
Out of curiosity, how can one compare their shields and armor going "strictly by the numbers"? The CIC database lists the WC2 Rapier as having 11.5 cm shields and 7.5 cm armor, whereas it lists the Hellcat V as having 250 cm shields and 100 cm armor. Is the database wrong? I always figured either there was a major advancement in both weapon power and shield/armor thickness between the two games, or a unit was misplaced (i.e. the WC3 database should be in mm, not cm)? Where are you finding numbers that allow you to compare the two ships?