I find it strange that apparently due not being based on early kills or necessarily spacing tippers, Lucina is "for casuals" . She shouldn't be weighed by her mechanics in comparison to Marth - and debating who's playstyle being better would be strange as both are clearlydifferent through their mechanics in their falchions and thus give leetway to several different playstyles for many types of players.
As it seems now, she's for the players want to use Marth's shorter range and spacing in Sm4sh to do consistent, reliable damage/knockback and better comboing rather than go for tippers and early kills with chances to be thrown off from the flow by either non-tippered or tippered moves during fighting.
It might make her feel "easier", but sadly that'd be about as same as us having to restrict to rules or playstyles we're doing for sake of keeping dignity or status over the preference. It's rather immature to think we should play in one way (or character, even if superior possibly) only to win, when in general, anything can, and SHOULD BE used to win, especially if it strikes your fancy rather than all other people.
And from what I've seen, Lucina's playstyle is not something that has proven anything lackluster for those purposes, contrary to that even. (She'll be in competitive scene nonetheless, even if becoming potentially lower tier than Marth is)
I've been still trying to get into Marth but he asks quite a lot with his current playstyle and feels not entirely flowing or reliable as Lucina when it comes to playing in matches. This might of course, make Marth much deadlier under better hands, but saying we should keep choosing from double-edged sword all the time over the regular one sounds ridiculous to me if one doesn't like it, yet should be labeled casual.
I'm not too big Lucina-fan myself (actually I'm more of Marth's), but still, I'm playing her due feeling more balanced and reliable. And if it helps or encourages me more to win than using Marth, then that definitely is better than having to pick up someone that I just don't feel clicking to with while there's more preferred - heck, better choice in my hands.