Energy boost can cover everything for energy. I didnt touch a sigil til lv 175, only have 200 now(because I couldn't sell so I used)Mages need insane energy regeneration, so you wind up spending tons of points on energy well if you are poor. When you do that your dps hurts so bad everyone is motivated to buy sigils instead. By end game if you don't have 2-3k energy sigs you will be way behind. Also when mobs sneeze mages die - mages and rogues top the deaths leaderboard. If you use energy well, freeze and eshield you are no dps lol.
Energy well is a horrible skill, would never touch it, I'd argue spring of life is better.
But the points for energy boost are to spare usually. Say you are 120(119 skill pts), you have 29 in bolt 29 in storm 29 in attune 14 in lure. That's 17 spare on the new cap(new cap so as you level toward 150 you get more points til cap increases again). So boost can be 18 which is good enough. So dps is not harmed but you won't have an e shield. If you want shield you have to dock out points, level up, or split the boost.
As for health. Yes mages die easy but if you are careful(not running into aoes, not ice blasting everything, not taking on 4 stars with low hp) you will win(unless you miss). But as prove to it, I leveled 1-110 full focus, 111-190 with 1k hp. I'm back to full focus again.