Godzilla (2014) and Kong: Skull Island both made well over $500MM each on around $150MM budgets a piece.
KOTM was the weakest take so far (somewhere in the $400MM range), but still more than doubled up its budget.
It'll at the very least, get this sequel, but this leg of the franchise is fading.
Screenrant actually had a really good article about the Monsterverse a couple of days ago as well:
Your numbers aren't quite that accurate but not far off. From my understanding, profit for movies really comes into play after you make back double your budget. The budget counts for the movie but doesn't factor in the ad campaigns and such. Plus obviously theaters take a chunk of the profits as well. KotM was...not a success but not a total failure, either. I read blu-ray sales have been really good, though.
Godzilla 2014 - Budget: 160m Worldwide Gross: 524m
Kong: Skull Island - Budget 185m Worldwide Gross: 566m
King of the Monsters - Budget 170m-200m Worldwide: 385m
As for the leaks...not a fan of the design but not dismissing it until I see real pictures and not some cheap toys. I hope they use the skeleton of another of Godzilla's species, though. I totally still expect Ghidorah to be in it, too.
I imagine it going:
Kong vs Mecha (in Godzilla costume) - Kong loses but exposes it
Godzilla shows up and wins against Mechagodzilla but he escapes somehow
Ghidorah shows up with it's own Mecha parts and beats Godzilla
Kong and Godzilla team up against Ghidorah and struggle.
Mecha Godzilla changes sides and it sacrifices itself in some Millennium Kiryu sorcery
I'm totally wrong but that's my imagination running wild