Exactly - the earth cannot be round without gravity. Its the cart before the horse. Lets presume the earth is round then come up with a theory that stops us falling off it.
Actually, the earth was known to be round for around 1500 years or more before Newton came up with gravity. Before that, people believed that things fell for much the same reasons that you explain: because that's what heavy things do. Newton's version of gravity describes, with pretty good precision, how heavy things fall the way they do.
And you mention 'credible explanation'. That doesn't meet the 'beyond a reasonable doubt' test.
Science doesn't use the "beyond a reasonable doubt" standard. It uses the "preponderance of evidence" standard, and that standard is much higher than you probably think.
A couple of questions if you don't mind. From a science perspective; if gravity did not exist and as a consequence let's say that everything floated 'on air' so to speak. Would it be fair to say that science would then want to know why things floated and why they did not fall to the ground (as opposed to why things do not float and do fall to the ground)? And if so why would we think there was something preventing us falling (as we seem to wonder why we don't float for example)?
Gravity Equation is plagiarizing Coulomb's Law
Gravity Constant G is equally Coulomb Constant after unit conversion