Very soon you might realize, that Twitter is good not bcoz of frontend but the major tech expertise is in the backend systems to handle super high traffic and dispatching messages quickly.
WTH!
Either start as Mobile only app and be successfull (Eg: Whatsapp)
(or)
Start a Website and gradually introduce mobile apps (Eg: Google)
(or)
Start a retail service, use website as entry point, then introduce mobile apps (Eg: Amazon)
Myntra model is backwards. Start retail, use desktop website, start mobile site, think about mobile app, hate desktops, shutdown desktop website, shutdown mobile site.