I like the edits. I still think it's very potent. Again, if the goal isn't necessarily to have a balanced race, I think it's fine. D&D doesn't always have to be about perfect balance. Theme and story counts for a lot.

The biggest balance problem remains the flight. I like the clarity around True Form (if you sprout wings, you're likely to get hostile reactions from friendly and neutral NPCs), but the challenge is that most D&D action isn't set in a friendly settlement. If the incubus is adventuring through X1 Isle of Dread or I1 Dwellers of the Forbidden City, he doesn't much care if the local head-hunters / dinosaurs / tasloi / yuan-ti see him in fiendish form. All he cares about is that he's chucking eldritch blasts and fire bolts from 100 feet up in the air, and he only has to worry about the occasional yuan-ti malison with a shortbow. Plus a few wandering pteranodons. To balance it against the aarakocra (for example), you either have to strip all those cool abilities which make it feel like a succubus (bad idea; theme is important), or you need to attack the root cause head-on. In this case, the issue is permanent flight (in most combat situations, where NPC allies aren't present) on a race that is tailor-made for being a ranged warlock or sorcerer. Perhaps limit the flight to X rounds per days, or non-functional wings that permit gliding only, or similar.

The key comparison remains the aarakocra. The aarakocra racial abilities are flight and 1d4 damage with unarmed attacks. That's it. No darkvision, no fire resistance, no spells, no shapechanging, nothing. Yes, the flight is faster than the proposed succubus, but that's moot. Once you're in the air, it usually doesn't matter if you're 30' up or 50' up. Unless the enemy has flight or decent ranged attacks, it's hosed. I know this isn't relevant in every adventure (the ceiling heights in the Caves of Chaos, from B2 Keep on the Borderlands, aren't really of any help to flying races), but it's still a significant design factor. It's a racial ability that makes some enemies completely irrelevant. For the aarakocra, their entire shtick is their flight. If they can't fly, they have nothing. For the proposed succubus, flight is just a by-line. They're still as good as tieflings even without it.

...maybe flight becomes a racial feat? Check out the treatment of svirfneblin in Sword Coast Adventurer's Guide. They start with fairly modest racial abilities, but can invest in the Svirfneblin Magic feat if they want to "unlock" the more potent magical features exhibited by the MM version of the race. Similarly, you could strip flight and suggestion from the incubus, and create a new feat called Heart of the Fiend (requires incubus/succubus race). Upon taking this feat, you gain the ability to fly for up to 3 rounds + 1 round per point of Con bonus; flight rounds needs not be consecutive (e.g. you can fly for 2 rounds in the first combat, and still have a few rounds left). You also gain the ability to cast suggestion. Both abilities recharge after a long rest. In that case, you could probably keep all the other racial abilities, and even remove the Strength penalty. I've never much liked ability penalties on races anyway, and pushing the more potent powers out to a feat seems like a good way to balance it.

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