I don't think it is a lineup shakeup that is needed...I think the pure and simple problem is that the FF need a GOOD BEYOND GOOD writer that can take a 'Back To Basics' approach with them, write the Core Four as they should be written by the textbook with no superficial 'personal' touches on behalf of the writer (such as unnecessary virtual 'rewritings' of characters' personalities and unnecessary retcons... *glares at Mark Millar and Matt Fraction*) AND the focus be back on THE Four and NOT everybody else BUT the Four. A grating problem with the book for at least me and I'm sure others, whether or not they are coming out and saying it, is that there has been and still is way, WAY too much of a fixation on the children and supporting casters like the Future Foundation kids instead of the Fantastic Four themselves. I've been saying time and again that the book's title honestly should be "The Franklin and Valeria Richards Show! Oh and Those Four Other People Too".
So you can finger the original FF all you want for poor sales, but it is honestly not their fault between the fact that they really have technically not 100% been in the spotlight in their own book for the last few years, had their comeback under Hickman ruined and some by Fraction and his terrible TERRIBLE (to say the least) interpretation, horrendous writing/handling of the Four through the last decade with two exceptions (Waid and Hickman), and Robinson trying to win back readers after they were turned off by Fraction's gobbledygook to the point of the worst sales in title history. If anything, finger Fraction for how he undermined Hickman's hard work in finally bringing the FF back to the fold...all the more reason I honestly (and very obviously) can't stand Fractoid.
The FF title has always had its best success with the Core Four...notably the Lee/Kirby run of course, Byrne of course as well, Simonson, Waid/Wieringo, and Hickman. Also there was out of left field minor success with the Wolfman (which didn't have the absolute best sales, but was and still is most certainly a critical success...not only said by many, including myself, to be up there with Lee/Kirby and Byrne as one of the greatest FF runs, but still sees reprint/graphic novel action time and again) and Lobdell (probably the bestselling short term run in FF history...a damn shame it didn't transcend three issues as it originally should have) runs. Every last one of those runs had the Core Four at their cruxes, and they all did well. All shakeups have been met with mixed reactions, often eventually leaning towards cries of wanting the Core Four back. Englehart and DeFalco's runs are PRIME examples of this. Englehart wrote his FF with the intention of Reed, Sue, and Franklin being permanently gone from the title...and the fan outcry immediately got to where Englehart had the nerve to 'voice' Sue in a pin-up (in FF Annual #21) saying 'she and Reed were amazed at some of the (then) recent letters!'.
It got to where Englehart was literally forced to bring the Richards family back, I.E. he was ridden out of the title on a rail by the fans AND Marvel...and, no I'm not afraid to say it now nor whenever this has been brought up, rightfully so.
But alas, DeFalco eventually came along...and rumor has held that if he'd had his way, Reed AND Doom's deaths would have been permanent. Thank Jove that did not stick. IIRC, the only reason such malarkey and the lineup shakeup caused by it happened was because DeFalco was not keen on writing Reed and Doom. Well, his 'back from 'death'' Reed was really not all that terrible, and dare I say, probably the most bada** Reed found himself being since the Byrne run. BUT, and yes, it's purely my opinion, but DeFalco's run was a step below mediocre with the Core Four, and the lineup shakeup (AND removal of Doom) really did not improve things much at all...a GREAT example of my grand argument that it's not the lineup, it's the writing, THE BLOODY WRITING.
Which, in conclusion, Robinson is certainly a massive improvement over Fraction, but at the same time, he's not Byrne or Hickman. They have been THE last scribes to have, to varying degrees, a virtual sixth sense as to what make the Four tick more above and beyond the others who have taken on the Fantastic challenge in the last decade. Yes, even Hickman despite my constant gripe about his ridiculous over-reliance on the chillins...but I'm much more willing to let bygones be bygones there because of how exquisitely well Hickman handled the Four when they were allowed their limelight (as well as give Reed the most positive spotlight he has seen since Byrne). But you can toot the shakeup horn all you want...it would only be a band-aid at best. What is really, REALLY needed is a miracle salve in a writer that has the said virtual sixth sense, has it in themselves to utilize timeless elements of the Lee/Kirby, Byrne, Wolfman, and Hickman periods and eras; and bring the title back around to where the Four are THE stars with the supporting casters not transcending their sideline roles and being ball hogs.
*literally bounces off of her Richards(TM) FantastiCleanser box and out of the room*