It really does not mean that. It means it's not AS OPTIMAL as a stat increase some times, but that is not the same as being "just a filler". Can we tone down the hyperbole a tad? There is a range which lies between "meaningless" and "exactly as good as the average use of an ASI in your primary stat or the four best feats in the game." Let's talk about that range as it really exists for most people who play the game rather than treating it as a black and white issue where everything neatly falls on one side of the other.
Sure. Here goes.
I want flavorful feats that are as good or better than a primary stat ASI, because I like flavorful feats, and I don't want them to be trap options.
I don't want them to be trap options, because I have seen what trap options do to gameplay. I play with, and intend to play with, people with a variety of approaches to charop. I don't want people who don't care about, or don't work on charop, to take trap options, and experience the side effects.
Static ATK/Save DC bonuses are deceptively strong in D&D, and what I find in actual play is that when monsters scale with total party competence, players 2 points behind on ATK/Save DCs experience a lot of frustrating wiffs.
Picking flavorful feats ends up being a trap option. Not a huge trap, but it does accumulate.
So I want fun, flavorful feats that compete with a primary stat ASI bump.
This makes taking these feats at level 4, in place of the only ASI you get as s non vhuman in modt campaigns, a character-story boosting moment
and one that isn't a trap.
To that extend, I prefer players taking XBE or SS to +2 dex, as it provides more texture to the PCs. I don't want +2 dex to suck compared to them, because it should be preferred by people who want to keep it simple. Or who want a "I am inhumanly dexterous" as their character story, not "maxing dex is a no-brainer, and not doing it requires serious charop to make up for without becoming less competent".
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This is why I want every single feat to be something you can hang a character concept on, both thematically and mechanically. I also want them to be flavorful.
So, take Keen Mind and Linguist. Add them together. Call it "Savant". Add in the ability to read spell scrolls outside of your class with an Intelligence check (DC 10+Spell level).
That feat is getting mechanically sizable, which is annoying. But a character who takes that can hang a character off that, both mechanically and thematically. They have 3 extra languages (sometimes useful), a bunch of ways they can demand info from the DM (perfect memory, direction, time), and can collect scrolls to have a bag full of interesting tricks at their disposal. (I'd honestly cut the cipher rules, because that is the kind of thing you should be able to do without a feat)
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Is that feat as "good as crossbow expert"? I'd argue you really cannot compare one against the other.
But a rogue with Crossbow Expert and a rogue with that combined "Savant" feat will feel different at a table, which is what I want, and each will be significantly better at their area of expertise than the other. The areas of expertise will be significant and should show up in most games as well.
A charop person might be tempted by it instead of XBE. It optimizes for something different.