For tier-2 and tier-3 cities where airtel/jio broadband isn't available, how can I get stable, high-speed internet connectivity? Local ISPs are good but the internet dropping during meetings screws things up.

BSNL is reliable in such areas.

My area is outskirts of delhi so BSNL is not available. :/

Some one had written a detailed post in a past to install antenna to get good speed over a sim card. I don't have a link of it, but I wish someone or author can help with link.

Is it this https://suraj.dev/blog/my-4g-setup-for-working-remotely-from-anywhere?

Get multiple connections and a load balancer like R480. Other options: mikrotik, ubiquiti edgerouter, pfsense / etc (on own hardware).

Does a dongle work better than a phone hotspot?

Jio dongle.

ask nearby phone recharge guy, they have best details of the area you are living