I was going mostly around Kingdom because I owned more kingdom 4*-5* cards then others but will recommend against limiting yourself in 1 faction, the main reason would be you are skipping other great cards by narrowing your deck to a specific type and also limiting your runes.
Runes can be game changing I personally love:
Arctic Freeze (gives ice shield)
Permafrost (casts blizzard)
Thundershield (gives retaliation)
Tornado (casts lightning chain)
The way you play with your runes is as important,runes have a counter on how many times each can be used. So holding back 1 card to hold back your runes from triggering too early can be great. (i.e. casting a kingdom card turn 1 will give you ice shield for 3 turns after that card dies but keeping your card till later will give you ice shields in later turns which will most likely protect your late game cards better. Blocking more damage.)
Also waiting at the start of the match and playing 3-4 cards on 1 turn instead of 1 per turn can be devastating and give you a advantage.
Just make a deck including all your solo strongest cards (cards who are good on there own regardless of faction) and go from there.
If you could give me a list or captures of your 4-5 star cards I could give you a deck build and see where you stand better.