this statement is logically incorrect - if the 'jury is out' on aspertame, when it 'reconvenes' it could discover that it is worse for you than HFCS, and so no, in fact, the prophylactic switching that you speak of would in fact be detrimental.
Anecdotally, I feel much worse on 0cal/diet beverages than HFCS equivalent - the 0cal/diet ones seem much more likely to trigger headaches/inflammation in me, though it could be that I don't "think" i need as much food so I actually let the diet drink facillitate bad nutrition which in turn triggers these things ... probably the real 'safe bet' is to switch away from both regular and diet soft drinks, since HFCS also is not good
It's hard to say whether aspartame is worse or better than tea and coffee.
"[it takes] as much as 132 gallons of water to make a 2-liter bottle of soda" https://www.wsj.com/articles/SB123483638138996305
If you do the math, a 2-liter bottle of soda = up to 250, 2-liter bottles of water