Can Sweetie Belle still sing really well? Is Scootaloo still good at doing stunts on her scooter? Is Apple Bloom still good with carpentry/building/inventing/alchemy?
but seriously. they've known that they were good at those things.
but they never got their marks for it. even though those WERE their individual marks, they didn't realize that they had a shared talent, one they didn't really start doing until much later, after they had already tried out these tons of things...and learned more about themselves in the process, Diamond Tiara even points it out...and until they had enough experience and had done enough self-searching to realize that others have issues knowing themselves, so they helped them find themselves the only way they knew how, by thinking of the situation...alot... which is exactly what they did when they were crusading.
that's when they discovered what the final puzzle piece was.
In essence, their search for their special talent caused them to know themselves much better, which helped them realize that others have not searched themselves as much, so, using the self searching skills they learned by doing all this shit, they developed a talent for guiding and helping others.
>in a plotline not shown in the episode, the griffin kingdom has declared war on Equestria and is killing the shit out of everyone
>Luna resorted to the age-old tradition of conscripting all those without special talents as meat-shields via a huge spell nobody remembers existed
>all blank-flanks in Equestria are now official "Shieldponies" and will be rounded up and sent off to the front lines
>this is why the cutie marks look so similar and bland
And thus the story of the CMC ends, no more episodes with them no takebacks permanent.
cutie mark =/= skill or talent
it only represents your greatest drive or purpose, which could virtually be anything
what drives the CMC is pretty clear by the end of the episode
and with that in mind, you could say they gained such similar cutie marks by sharing the same motivation despite having different aptitudes and preferences