As expected, yep those videos are very very old. i am gonna copy-post some previous answers to help you out.
1) Read the beginners guide to SH: https://www.reddit.com/r/SoulHuntersGame/wiki/newplayer
2) check out reddit's Q&A FAQ thread: https://www.reddit.com/r/SoulHuntersGam
3) check out the Wiki for specific and mostly general info: https://www.reddit.com/r/SoulHuntersGame/wiki/index
4)Check out hero viability and tier list by ZiOiP: https://docs.google.com/spreadsheets/d/
5) A cookie butter team for Arena: Zem, Taurus, Xanos, Lumos, Firehawk
6) A cookie butter team for Campaign: Zem, Taurus, Xanos/Lumos, Jasmine, Firehawk,
7) My guide still incomplete but better than nothing and the COF section is pretty decent: viewtopic.php?f=18&t=12026
8) Heroes considered good by Most of the players and you can upgrade them without hesitation: Zem, Tashi, Taurus, Kong, Xanos, Nilya, Lumos, Serafine, Jasmine, Firehawk, Blood spear, Ling Ling, Goram, Sylphi, Desmond, Ezio [7* only], Desmond. this list does not include HOL shop heroes.
9)This was a pre-generated answer if your still having problem please comment back.
10) If you received no answer or an unsatisfactory answer go ask at Sh subreddit's weakly Q&A thread as well: https://www.reddit.com/r/SoulHuntersGame/