The question each one answers
Shopify answers how to own a storefront end to end: domain, checkout, payment processing, apps for everything else. It is built to be a destination, and the work is bringing people to it.
A Telegram Mini App answers something narrower. If the people who buy from you already read your channel or sit in your group, the shop can live there, one tap from the conversation, with nothing for them to install.
Where the jump costs you
Every step between a message and a checkout loses people. A link out of Telegram into a browser, a page load, sometimes a login. For a shop whose whole audience arrives from chat, that jump is the single biggest leak, and it is the thing a Mini App removes rather than optimises.
Where a standalone shop still wins
If most of your traffic comes from search, comparison sites or paid ads, you need a public storefront that those channels can point at. Telegram is not an index and a Mini App does not answer a search query.
Complex catalogues are the other case. Thousands of variants, heavy filtering, and an international tax and shipping matrix are what a mature platform is for.
Cost, plainly
On the Mini App plans, BotLaunch is $0 for up to 10 products and 150 orders a month, $19 for up to 100 products and 1,500 orders, $49 for larger catalogues, and $99 for unlimited products and orders. Orders are seller-fulfilled by default, so there is no processing cut on top. A platform with its own checkout charges for that checkout, which is fair and also a real line in your costs.
Running both
Plenty of shops do. The Mini App takes the audience that is already in the chat, the standalone shop takes everything that arrives by search. They are not the same customer and they rarely need the same catalogue.