Nostr requires more data than traditional socials because it is not a specific platform with its own dedicated servers. Regardless of which client, you are connecting to many relays, each with its own availability, latency & other capabilities. Media is not downgraded to achieve minimal storage, your notes are not altered, etc.

As for your buggy reply experience, things are improving but this does still happen on occasion. Some relays may always be difficult to connect with in low-signal environments. Sometimes opening your client and waiting a few moments can help.