I think there is a wide range of "busy", what does it mean here? How many people do you usually meet in July on this trail? 10, 30... 200?
On a sunny summer weekend it will be over 200. This is prime reason why I don't like Berg Lake Campground -- too many people, some of them loud, inconsiderate, etc. But on shoulder season, midweek -- if you get lucky with weather -- it can really be magical, the way it is supposed to be.
Don't let any of this deter you. Go with open mind and enjoy. Since you are dayhiking from Whitehorn you can do very nice loop. Follow main trail to Berg Lake (with mandatory side trip to Emperor Falls). Note marked junction at Marmot Campground. This is where your loop will end. Proceed to Berg Lake Campground , then take Toboggan Falls trail. It branches off near the shelter. Follow up, then when you reach junction go left (Hargreaves):
This will eventually bring you back to main trail at Marmot campground, but you will have some awesome views of Berg Lake from above:
as well as Hargreaves glacier, that 90% of Berg Lake backpackers don't see:
This part will be considerably less busy and will feel like real wilderness. Trail is good and you can't go wrong anywhere. Total for this loop from Whitehorn return should be 8-9 hours, with light daypack.