Regarding the overhead thing specifically, there are some cases where it’s not entirely clear if a player got hit because they were guarding low, they were being frame trapped, or if the move was straight up unblockable anyway. The worst offender I know of this is C/H Kohaku’s 236[A], where it looks like a low, but the charging implies unblockable, but it actually becomes an overhead. Yeah, after getting hit by it four or five times, a player could probably figure out that there’s something going on there, but the fact that it’s an overhead precisely could stand to be better communicated.
I think the other part about fighting games that make them kind of unappealing for more casual gamers is the fact that when one player is losing against a considerably more skilled player, there’s a very strong feeling of helplessness. Even if it isn’t a strict slippery slope like chess, getting continually knocked down or punished for every unsafe move thrown out is incredibly demoralizing, especially when there’s so much that a player needs to learn in order to not be put into those situations (asymmetric design). Compared to a FPS where even if a player gets headshot continually, there’s still a feeling of chance of getting that one lucky shot, especially when one ‘life’ is worth so much less than an entire lifebar in a fighting game.
This is kind of like when Magic had a problem with Affinity dominating standard as opposed to Caw-go (or Caw-blade). For those not informed, the Affinity deck was an incredibly oppressive deck that was hard for the other player to play against because it took control of the game so quickly and made it feel like one player couldn’t do anything about it. This feeling was made worse by the fact that the deck was ‘easier’ to play than most. Caw-go on the other hand allows the losing player to still feel like he or she is still playing Magic, even if only to just be crushed under the weight of continual card advantage. Furthermore, the deck tends to require more skill. Both decks were eventually gutted by having their key cards banned in the end, although it took a while for Caw-go/blade’s Jace.
So how does this tie back into casuals in fighting games vs. other genres? The casual player fighting the more knowledgable player in a fighter is like going up against Affinity. There’s less ‘perceived’ interactive skill in continually being hit while on the ground, continually mixed up,continually comboed, or continually punished even if a lot of calculations and skill goes into reading every move and countering it. Additionally, the player getting hit by all these things can’t really do anything about it until he or she just gets better. Compared to a FPS, every time a player gets headshot, there’s always a feeling of skill involved, so a player doesn’t feel as bad being defeated. Also, in most FPSs, every time the player dies, he or she gets right back up in 5 to 10 seconds to try again and to start playing the game again. There’s still a feeling of playing the game, like in Caw-go, even if the player is still going to inevitably lose over the continual score advantage the other player is getting, or card advantage.
Tl;dr: Fighting games are not fun for a casual player when playing against experienced players. FPSs still manage to be somewhat fun in the casual vs. experienced matchup.