RA differences were more subtle and situation based, but they were definitely there.
RAmar was a workhorse using Spread Needle (or a custom Needle with seize) and Snow Queen to disable everything possible.
RAmarl was the support RA able to use level 20 SDJZ and Resta to best keep a cast party moving.
RAcast had the highest ATP, so he was the DPS RA of choice and good ones abused this in groups with high damage mechs (like Yasminkov 9ks, Guld Milla, etc)
RAcaseal had the highest DFP and extra traps, so while she is probably the worst RA in terms of Ep1 and Ep2, the trap bonus and high defense made her great in episode 4 for being able to whip out a Custom Scythe on lizards without leaving the party gimped against Pazuzu and friends.
RAmarl was also good for having ridiculous TP and being able to solo better than any other class thanks to level 20 techs and the Heaven Striker set.
While I’m at it, the FO difference is mainly based on tech choice. There are some people that liked going melee FOs, which is fun and all- but ultimately not very good.
FOnewearls- (FOneys) God, I hated this class. Major boost to the basic level attack techs, had the highest MST in the game which made them good at all points in the game (and especially insane in Challenge Mode). This FO class is second best support (high MST = super Resta) and second best nuke (Foie and Zonde were great at nuking things that needed to be nuked and being basic techs means they cost very little to spam).
FOnewms- Why did all of their costumes have to have that gigantic ass? I really saw no point in that. Anyways, best nuking FO in the game thanks to the RA-level boosts, probably 4th in support just because you’re going to be wasting so much TP on nukes that you won’t have enough to effectively support in all phases of the game.
FOmars- If I saw one more FOmar charging into a mob with an Excalibur with Tellusis mag, I was going to puke. Obviously a popular choice for whatever reason, they were bad at nuking despite a boost to Gi level techs because Gifoie is the only one worthwhile, and that was awful later in the game where the main point of nuking is to keep enemies in hitstun (Probably the worst) and were pretty lacking in the Support department thanks to low mst.
FOmarls- Best support class, had a huge range boost to SDJZ and a strong Resta to accompany it. Also had the highest FO ATA which was mostly irrelevant until late game when you could combine the Sweetheart Set with Slicer of Fanatic to do some major damage or with Vivienne to keep your TP filled. Best Support, but poor nuking abilities (although the 125% Grants damage was amazing when it was relevant).
Generally, the optimal team for end game was a support character (generally a FO unless you really can’t find one), a disable (generally RA with Spread, although the higher ATA HUs could accomplish this pretty well with a Red Sword with hit %), melee DPS (usually HU), and a ranged DPS for things that couldn’t be disabled or are otherwise problematic like Zus (usually a RAcast, RAcaseal, or HUcast with charge mechs). When trying to get that setup, you can see where the different classes specialized in different roles. Your RAmar would usually sit in the disable role, but could definitely play support in a party with a HUcast, RAcaseal, and HUcaseal.