Back in the day, telepaths weren't as powerful as today. All the mind control, psychic blast, make your heart stop, reprogram your mind to teach you all the skills and languages in a second, etc. stuff came over many years, as one-off feats by one singular telepath (like Xavier) and then just sort of trickled down to every other telepath (even DC telepaths like Saturn Girl and Martian Manhunter!), because the writers had no idea that these were supposed to be amazing feats by only the best telepath in the world.
Back then, Emma had to use a machine to swap her mind with Storm's, for instance, a feat that even a decade later, she could just arbitrarily do, with Iceman.
So it's entirely sensible for Emma to not have been able to do anything to Shaw, back in the old days, when she was primarily a mind-reader / thought-sender. He was bulletproof, and she didn't have her diamond-form to immunize her to his brutal strength. Once she developed the full raft of powers that come with being a comic-book telepath, like mind control (Karma's entire power), stealing skills (Prodigy's entire power), illusions (Mastermind's entire power), astral projection (Scanner and Trance's entire powers...), etc. then, yeah, it makes sense that she'd be in charge of any group she *wanted* to be in charge of.
But even then, much like Exodus, who was vastly more powerful than Magneto, and yet still chose to let him be in charge for a time, it's also entirely possible that Emma recognized that the Hellfire Club was a pit of sharks, and she didn't necessarily want to be the one target they were all gunning for, but more of a 'power behind the throne' sort of figure who gets things done, and isn't dodging 24/7 usurpers and assassins coming for the king...
That all said, it's utterly perplexing even got away with *planning* this, let alone carrying it out, in the modern Krakoa, which, according to Jean, has at least thirty telepaths. (Then again, Morrison seemed to think Shaw *was* a telepath, even better than Emma, so perhaps he's got a secondary mutation?)