Yes, it does take more then "just a rock" or "natural erosion", or similar generic terms that don't convey much info. But, the difficulty that presents itself is that we cannot teach you face to face, live, handing rocks back and forth. It is actually a truly formidable task to elaborate lessons in a virtual format. It's actually extremely difficult.
Another "problem" that presents itself is that for experienced collectors, knowledge has become second nature, so that recognition as to whether rock or artifact can be near instantaneous, yet, because it is second nature, born of years or decades of experience, the original logical deductions and thought processes that produce answers are not easy to reconstruct for experienced collectors. That's what happens when knowledge, understanding, and recognition become second nature. So, while I can understand your frustration with "natural erosion", sometimes these brief, non detailed, answers are all that is possible in a virtual venue. It really is not our fault. To a great degree, the venue dictates it. It's far, far better when the rocks, artifacts, and teaching can take place in person. And explaining geological processes like erosion just ain't easy in any venue.
If you don't get the answer you prefer to get, you just need to live with it. People are still simply offering honest opinions, most based on experience. You can doubt the answers you receive, file them away, and continue to believe what you wish. Maybe the groove is man made, maybe it's a broken artifact that none of us can recognize as such from your photos. Maybe opinions would differ in person.
