Vistara infinite is the card you should be comparing the Magnus with.
Vistara will be expensive considering there are no offers and you’ll have to pay the whole amount. The business ticket only you can guess its value to you. Spend 100k and you’ll get additional 10k CV which is nice. But the future of the Vistara FFP is uncertain due to the merger.
In the VS the reward rate will further go down, its basically a premium economy ticket that you’ll be paying 3k for.
Magnus is definitely the card you should get. Effective cost at the worst is 3-3.5k at max. Many opportunities to earn ER via Gyftr and Grabdeals. BMS, M&G, unlimited dom & Int lounge access, plus the actual reward ratio, no matter if you achieve the milestone or not is more than VI. If you’re eligible, then hands down the Magnus.