Out of combat, this isn't even as good as the 1st level spell find familiar.
This sort of application of beast companions isn't all that creative. It's how wizards have been doing scouting for years with the find familiar spell. And honestly, find familiar comes with some features that make it superior for out of combat use. Here are some of the highlights from the spell description:
- While your familiar is within 100 feet of you, you can communicate with it telepathically.
- Additionally, as an action, you can see through your familiar's eyes and hear what it hears until the start of your next turn, gaining the benefits of any special senses that the familiar has.
- As an action, you can temporarily dismiss your familiar. It disappears into a pocket dimension where it awaits your summons.
- As an action while it is temporarily dismissed, you can cause it to reappear in any unoccupied space within 30 feet of you.
- Finally, when you cast a spell with a range of touch, your familiar can deliver the spell as if it had cast the spell. Your familiar must be within 100 feet of you, and it must use its reaction to deliver the spell when you cast it. If the spell requires an attack roll, you use your attack modifier for the roll.
Beast Master Companions don't get any of this cool stuff, and this cool stuff is a day 1 feature for wizards.
This is the cost of doing business. Don't nerf your ranger's cool features.
In my experience, what you describe is pretty typical D&D stuff. I've never been in a game where this sort of thing didn't happen. We even have a question about it: How do I handle a player exploring the entire dungeon with his familiar? Much of the guidance there is helpful and relevant to your situation, but I would offer one particular quote from Kotrin's answer:
If you're not comfortable with the situation, you should discuss it with the Warlock player to find how important those features are for him, and if he/she accepts altering his character because you are not comfortable with the situation, despite the PC 100% following the rules.
If this sort of thing is truly causing issues for you as a DM, talk to your ranger and work something out; but I would recommend rolling with it. Your ranger has taken this subclass for this feature. I'd recommend against nerfing it, especially since it's already not as good as a 1st level spell.