It is... Any change is adding to something. Whether that be through subtraction or addition. I get where you're coming from and where the to add people come from... It's just a silly addendum that was added post hoc because of silly populism. ETA is already established as estimated time of arrival. There's no reason to also try to rethink a common acronym. Beyond that, there's also no reason to signify what you added, or where. You can sure just use ETA to add anything directly after while leaving your OG comment the same, but nobody will know what you edited anyway unless it's an instance that records that stuff.

I think it's the same argument as debating whether nothing is something at the root.

Even then, it's a superfluous addition when you have to specify okay I've only edited anything after this ETA when the definition means you could've added anything anywhere.

Edit in addition, edit after comment, any variation leads to the same issue. It's just... So... Pointless.

It even takes more keystrokes! Whether you use capslock or shift for Edit: or ETA: l. E: Is just so much better.