TOTP in Bitwarden (or 1Password or KeePass) is an upgrade over SMS authentication in terms of both security and convenience.
For most people, TOTP in a dedicated app is not actually much more secure:
1. They could lose the device. Without a backup, they're suddenly unable to login to their accounts. 2. Their device may not be well secured, e.g., either not requiring auth to unlock it or only having a 4 digit PIN. 3. They're likely logging into accounts on their phones and have the password manager and TOTP app on their phones as well. 4. If the TOTP app has backups, then it's vulnerable. 5. Such a user may be less likely to use 2FA in a given app because it's less convenient.
If you secure your devices with long alphanumeric passwords, secure your password manager with U2F / WebAuthn and an even longer alphanumeric pass phrase, and consistently enable TOTP 2FA, then you'll be more secure than the person who either uses it less consistently or who uses it on device
Yes, you would be more secure if you used it consistently AND had 2+ dedicated devices for your TOTP codes (your main device and at least one backup). But let me propose an alternative: do that just for your most critical accounts, but use your password manager's TOTP solution for everything else.
Which dedicated device would I recommend for storing your TOTP codes? The same one I recommend for U2F, the Yubikey 5 series (specifically the Yubikey 5C NFC). It can store up to 32 codes, which for 99% of people is more than enough for all of their critical accounts.