The largest dinosaurs, sauropods, had zero adaptation for any sort of an aquatic life and nobody believes they lived in water any more. For starters, they would have needed snow shoes; the feet they actually had would have gone straight into muddy river bottoms and they would have spent their entire lives standing in one place. Likewise their teeth show the wear and tear of eating branches and leaves, you don’t get that from soft aquatic vegetation.
You were arguing that gravitation in the Earth has some how increased in recent eons making it impossible for creatures much larger that elephants to have survived...I don’t know how much I agree with the plausibility of your opinion but I was just trying to reason it out. We have water creatures much larger than elephants, so I was just playing around with your opinions. I was trying to give you the benefit of the doubt.