I personally hold this game as my favorite and I a very grateful for the things that it added, like navigating the map, buying weapons and items outside of chapters, and extra areas like ToV and LR. I don't see how any of these inclusions would make the game worse than other entries. If it bothers you so much, don't use it.
I think the reason why people think this game is so easy is because of Emulators and the use of save states. When you have an actual GBA and a single mistake you make might end up having you restart a chapter? Yeah, that's not fun. Sacred Stones allows you to either train or proceed with the story depending on what you decide.
If you want a challenge, try Hard Mode. On an emulator you might not even notice the difference, but on a GBA it's a different story. I am grateful that Hard Mode is challenging enough while not being overly frustrating. If you really want the frustration that was present in the previous entries of Fire Emblem, then yes, you might have to find your own ways to make it so.
I guess my point is that a game being easy is not a legitimate reason for it being bad.