Well, let me first preface this by saying, I think CoC is overall a bad/terribly obsolete 1980's vintage game system that should be retired forthwith and which I will never use again!
However, it does portray Cosmic Horror by presenting a managerie of creatures which are both horrific in aspect, almost universally lethal, and either hostile or having entirely unfathomable motives (and thus often acting in totally unexpected ways). PCs are physically MUCH weaker than all but the most trivial of monsters. Monsters have abilities (and cultists have access to them) which are entirely outside the realm of anything that PCs have (which is basically limited to the abilities of normal humans of the 1920's or maybe modern times if you play in the Cthulhu Now! module).
But I think SAN really IS an integral part of the 'flavor' of the game, and what made CoC such an iconic game.
Finally, CoC is a poor game mostly BECAUSE its process is so much like D&D! It is exactly the ways it is like old-school RPGs that are its weak point. The skill system is extremely hard to use, there is no context in which a skill operates, it is just a check called for by the Keeper, for whatever reason. Success doesn't really mean much, it just means you might be called on to make the exact same check again 5 seconds later. Or failure might not really lead to anything different from success. There's no indication of what is an appropriate consequence for failure, and being primarily a mystery type of game that EASILY leads to catastrophic fail plot stoppers and subsequent awkward plot bandaids, and characters that come across as idiots.
Making it worse, the skill system is open-ended. So there is an INFINITE LIST of skills. Many of the ones included in the game explicitly overlap to a very high degree, or are not clearly any better than your basic education or intelligence. While there is a 'levels of failure/success' rule it doesn't really clarify much either, and is often pretty much impossible to actually use. TBH the skill system is literally WORSE THAN NOTHING, and doesn't add anything to the actual subject matter of the game, quite the contrary (Mythos skill being the one exception due to how it interacts with SAN and its obvious thematic purpose). Seventh Edition's design clearly shows that Chaosium knows about these issues, they pared back the skill list some, etc. but it is far too little, and they failed to add any sort of mechanics to produce the sorts of dynamic escalating tension sort of play that happens in something like Dungeon World. A need that this genre BEGS the game to introduce.
Contrast this with Trail of Cthulhu, which does ALL of these things far far better. Its resolution mechanics are geared specifically to failing the game in a forward direction and upping the tension, and it handles mythos material and the mental effects of exposure, etc. just as well as CoC does. It is a 1000% better game. That is, it is a pretty solid 21st Century RPG design! This is really my ultimate position on this whole topic, is just that 5e is ESSENTIALLY a 1975 vintage design, with a few superficial add ons and tweaks. in the last 46 years a HUGE amount has been learned in terms of techniques to use in RPG design. Current game designs are simply a LOT stronger and deliver better play, more reliably, with less fuss. This is to be expected. Its fine to say you prefer your '57 Chevy, but trying to claim it is better than a Tesla Model S because you can run with glass packs and a 455cu in hemi head V8 if you want is missing the point entirely, the Tesla will still dust you every single time on the street, without fail.