My previous post wasn't particularly clear, so I wanted to try and clarify my point with larger comparison pictures:
1
2
Both maps are mirror symmetry KotH with two buildings flanking the middle point. In both maps, the building inland from the point has this ledge you can stand on, both detailed in the same manner. This particular type of ledge/detail doesn't seem to appear anywhere else in either map (although I have not verified this). My original point was that this exact detail in the same relative spot of the layout was beyond the level of similarity between Eros and Ilios that I'm willing to accept as coincidence.
However,
it doesn't matter. Even if there's elements borrowed from Ilios, it isn't a copy. Game devs (and really, creatives in all fields) "steal" from each other like this almost constantly, consciously or not. This very community preaches that you should be looking at Valve maps for inspiration on how to make your own maps. The only real difference here is that there was an existing "Overwatch will kill TF2" rhetoric to make people (especially the Steam Workshop) get real gross about anything that crosses between the two games.
That said, it's standard practice to acknowledge inspirations. Everything anyone ever made was inspired by something else, and any artists that seem to make totally original work are just very good at hiding their influences. "You're just copying x" is an easy target, and once you drop the pretense that your work is 100% original, your critics have to get more creative.
I don't think anything about the map itself needs to change. I can't comment on the layout since I've only ever played it in a sarcastic 3v3 setting, but this map is one of the best examples of how you can create a new theme (for TF2) with creative use of existing assets (and a limited number of new ones).
I didn't mean to make such a long post, but I wanted to try and exhaust as many parts of this argument as I could so that we can stop talking about this.