Early on it might not seem so much.
But the longer you are ingame the more time goes by with no energy spent.
Faction wars - I have 2 teams noew fcapable of tacklnig secodn boss, but it takes 7-10 minutes. 12 keys, means on that days I spend up to 60 minutes on faction wars.
Doom tower boss-silver keys - another 30 minutes.
I am in silver 4 arena with a counterattack team. Takes time to find profitable matchups and fight can take 3 minutes or longer - another 30 minutes at minimum.
3v3 arena - minimum 30 minutes to use up all tokens probably more.
That's about 2 hours playing the game with no energy spent.
Then let's assume it's item farm day. a progresed account can do dragon 16 but nott hat fast. assuming all dailies done and all advanced questss done that's 260 energy on top of your full energy. 360 energy means about 25 runs on dragon 16. 3 - 5 minutes per run that' another 2 hours.
So after 4 hours the daily energy is spent. Then you need to look at the items you got, roll them, decide to keep them or not, maybe glyph them. Meanwhile some arena markers have regenerated.
Also you are capable of doing mino 15, but not that fast. assuming you save gems for energy for mino 15. One run taking maybe 4 minutes. that's another hour or so of mino 15 runs for the daily gems. You get surplus gems from nm clanboss chests and events, another gem refill , another hour of mino runs.
All in all you now spent 6 hours in Raid without spending a single dime.
Then you can300 energy from the 3vc shop weekly (assuming you have drex) and usually 1k eenrgy weekly from the clanshop, extra eenrgy biweekly ffrom clanwar and incidental energy frome vents and tournaments.