I used to think that "monopolistic competition" is an oxymoron. (But more than 46,000 cites at Google Scholar.) I was stuck on "mono" meaning "one". It is actually about the impossibility of perfect substitutes and the fact that we each make personal judgements about which are the "good" vs. the "bad" substitutes.
So whether we shop online or the old fashioned way is not a simple choice. They are imperfect substitutes and each occasion involves a peculiar choice for each of us. This is elaborated in David Bell's Location Is (Still) Everything. The gravity law of retail gravitation is still valid -- and cities will not disappear. Coming almost 15 years later, Bell's book is the one to place next to Frances Cairncross' The Death of Distance.
The gravity formulation recognizes the friction(s) of distance as well as the attraction(s) of mass. Again, on a case-by-case basis we have personal subjective valuations of each. This includes whatever affinities or loyalties we may have for "first movers" into any product line. It also includes whatever agglomerations or clusters we choose to live in or visit.
No one ever said that marketing (or Tiebout-sorting) is simple. We form (and manage) networks in the real physical world as well as via the internet. Bell cites many examples where the uses complement each other. We often go online to help us with old fashioned shopping.
My major quibble with Bell's book is that he applies the Zipf rank-size rule to cities -- not the entire metropolitan areas. City boundaries are political and not functional. There is no reason for there to be a good fit.