Saying "just use Luma" is most definitely a bad thing, in my opinion.
Some time ago, a friend of mine asked me which cfw he should use (since there were no guides back then), and I took it upon myself to research CFWs, give me friend a tl;dr and when he asked for my personal suggestion, I'd say "well, what exactly do you want to do?", and we'd part from there.
A good while ago there were a few CFWs to choose from, we'd have RxTools, we'd have CakesFW, there was reiNAND, SaltFW, the back then named AuReiNAND, and Corbenik. Slowly for one reason or another, these CFWs died out, some were simply not updated (like RxTools), others were dropped for maybe personal reasons (like Corbenik), or maybe some were dropped for reasons unknown to us (maybe the devs were attacked by a few rotten apples?).
Currently, the only (public) CFWs that work with B9S (that I know of) are reiNAND and Luma3DS, at this point, Luma3DS offers a lot of features that reiNAND simply does not, I'm sure we all know about the recent Rosalina, or the ever useful layerdfs implementation of Luma, which with the ever increasing interest for Romhacks, would give the already popular Luma3DS a boost in popularity.
Why would you not use Luma3DS?
Maybe you've seen something in the code that you did not like, and thought you could go for something that implemented it in a "cleaner" way.
Maybe you just want a minimalist cfw that does something specific, instead of all the features Luma3DS will give you.
Maybe you just want full control over what features are and aren't enabled, as opposed to Luma3DS having almost everything enabled by default.
Maybe you're running your own personal little cfw.
Maybe X CFW has Y Feature that Luma3DS does not, but you really want to have (back in the day RxTools had builtin content decryption options, which many cfw would lack).
As of now, to everyone Running b9s, I would suggest Luma3DS in a heartbeat, but not just "because", but rather, because of all the features it contains and the fact that it is being updated constantly, and the devs listen to the community's feedback.
That said, I do agree that "just use Luma" should really not be the answer, but rather, "there is X, Y and Z CFW, personally I would recommend Luma3DS because...", not only are you suggesting your preference in a respectful way, but you would also be informing the user of possible options that they might want to research on.