It is stating that HikConnect will work instantly once configured and on the internet via P2P ports that are typically open on all routers. Remote live view and playback will work using p2p. But only once the ports are forwarded does it come off of P2P and uses the HikConnect
DDNS which allows for unlimited viewing time, remote configuration of nvr etc. This is the proper way to configure it.
Hikvision changed RTSP to 10554 a few years ago. All the new stuff uses that as the default port but may not be required in your case.
In regards to the port forwarding making your system vulnerable, yes that is true. I always change the ports to ones that are not the default to try and cut down on hacking. Also having a secure password (which is now a requirement for all hikvision devices, capital letter, symbols, and 8 characters long are now requirements within a password) makes a big difference. Ultimately anything plugged into the internet is vulnerable to attacks, just a fact of life. Honestly your router is probably more likely to be hacked than your NVR.
Sorry i cant be of more help to troubleshoot the problem! Not sure what else to try!