Well wouldn’t it be less tznius if the kallah wasn’t wearing a dress?
You don’t HAVE TO walk down an aisle, but you have to get the couple to the chuppah somehow. So that happens to be the most popular choice, currently, given the setup of most halls. If you choose to get married in a more chassidishe or laid back hall, you can have a chuppah on the street and just escort the couple through the crowd out to it.