Me...but certainly not Fox.
That's because you aren't Jeremy Slater. He's the guy who wrote the "less expensive" script and now Simon Kinberg is going to get all the blame. Him and Mark Millar and Matthew Vaughn for producing it.
Also, here's how I'd ground other villains
Mole Man - A depressive, near suicidal reject who's was teased about his short stature all his life who was driven to homelessness despite his brilliance. He rallied other bums dwelling in subway tunnels into a community and then discovered monsters living within the Earth's crust, giving him complete control over a subterranean civilization. It's more grounded since it's not just moloids, mole people are also citizens of Subterrania.
Annihilus - A being from a parallel universe. The Negative zone doesn't apply to the rules of our biology and underneath the helmet, he's a bipedal insect. We don't see his mantis face until his helmet is broken in the final fight.
Silver Surfer and Galactus - Galactus is simply described as a "god" by Uatu and he's a literal force of nature who does what he does for reasons that aren't disclosed to the audience. Silver Surfer is an alien who saved his world by becoming a herald of Galactus and is equal parts crazy doomsday preacher and apologetic alien invader who regrets what he considers to be necessary.
Trapster - He's just a mad scientist. I'd simply skip the Paste Pot Pete name entirely and then he's grounded enough for audiences. Wizard and Mad Thinker are simply mad scientists who don't require any work done aside from revealing Mad Thinker's real name.
Terminus, Terrax, Blaastar and Super Skrull are alien invaders. They don't need more grounding since audiences can just accept them as they are.
Diablo would be a molecular physicist who has the ability to manipulate matter on the sub-atomic level. That's how he perfected alchemy.
Puppet Master - Puppet Master would just skip the whole Wundagore clay thing and instead devise another means of mind control. At the same time, a Frightful Four lineup of Wizard, Trapster, Mad Thinker and Diablo is already good enough. Puppet Master can wait until everyone mentioned above is done.
Psycho Man is the only villain who's too outlandish for a grounded take on the FF and Hyperstorm sucks.
Point being, Fox doesn't need to make the villains mundane to make them grounded. The FF's rogues gallery only need a few small tweaks to be believable.