The best answer is somewhere between these two extremes, and I like your approach of starting simple and clear - a file based approach also easily lends itself to centralizing or bootstrapping to another medium - the bigtable approach calls for a migration and potentially even a change in the guarantees made by the underlying system because someone started to repurpose it as not just an audit trail because "of course we can just query it." (ugghgghghgh)
That's the extra complexity. If dumps into data lake are that important, then it becomes its own special beast that needs to be fed. If the dumps into the data lake aren't important, then the question to ask "Do I need the data lake at all or am I doing it because everyone else is doing it?" If the answer is "yes" then absolutely build that functionality. If the answer is "Eh" the question becomes much murkier.
In my experience companies are experiencing data overload and data paralysis because they have tons of data that is absolutely useless now and will be even more useless tomorrow. And they keep adding data about the data because that's the current koolaid everyone is drinking.