Sword of Spirit
Legend
So, what sources are actually available for options? Apart from the PH, I'm aware of Xanathar's and UA. Then, the setting specific options like the Sword Coast. I'm not familiar with Tashas...
One important thing to note is that none of the subclass options in Sword Coast Adventurer's Guide are unique to the Forgotten Realms. The closest to that is the Purple Dragon Knight, which suggests calling the class "Banneret" when used elsewhere. The others are all classic D&D fare, or new generic D&D subclass options. For example, you might remember things like Battlerager and Bladesinger from the 2e Complete Book of Dwarves and Complete Book of Elves (both generic non-setting specific resources) respectively. In like manner, it has the standard D&D racial pantheons (though Mordenkainan's Tome of Foes has expanded versions of those). When it comes to character options, outside of a few of the backgrounds and Ghostwise halfings, most of the stuff in there isn't Forgotten Realms specific. Now, the book itself is heavily invested in Forgotten Realms stuff, but they somewhat unfortunately nestled a lot of not specifically Forgotten Realms stuff in there and didn't reprint some of it elsewhere. So if you're big into options, you might not-setting specific options in there. (I feel like the options in the other setting books really are often setting specific, though most of them have at least a couple you could fit into a more traditional D&D framework.)
Another thing to be aware of that a lot of people miss, is that the listed Backgrounds are just examples. Right in the PHB and even the Basic Rules document they tell you that you can customize them, and precisely how to do it (basically, choose any two skills, any combination of two tool proficiencies and languages, any of the listed Features, and any of the listed equipment packages). This means any character can get proficiency in any two skills they want, for instance. I also like to point out that this isn't listed as an optional rule, but as a core rule. In fact, it's more core than gnomes and half-elves, which are listed as optional.
Of note is that it also contains some new spells, two of which the designers went on to state they feel were mistakes. They are Greenflame Blade and Booming Blade, cantrips that allow the user to make a melee attack and add other effects. If there's anything in any of the supplementary material that is unbalanced I'd say these are the closest to it.
Interesting. Do you have the source? I'm curious to see what their phrasing was. I find those spells to be essential components of my campaign, and think Eldritch Knight needs them as much Bladesinger.