##Change the rules##
Change the rules
Between identify, and the rules for characters figuring out what items do by spending a short rest with them (DMG p. 136), 5e is signalling to us that by design, figuring out what magic items do should not be a challenge. I can see the argument: from a player's standpoint, they might just want to use their treasure and not jump through hoops to do so; they feel like they've already earned it by finding / acquiring it. But as someone who is primarily a DM, I see the other argument too.
Bottom line: decide whether or not you agree with that aspect of 5e. If you do, just let it go, if you don't, change the rules. As-is, it is almost trivial to identify a magic item. You, as the DM, are well within your right to change rules. Doing it mid-game with a precedent already set is another matter. If you wanted to go this route, you could say that those techniques only work on, e.g. uncommon magic items (thereby saving yourself from this issue when the party starts discovering more powerful items). You'll have to make a judgement call regarding what change, if any, is appropriate given the established precedent.