Some ways I have used to keep "Glass Canons" from getting out of hand and frustrating the other players:
1. The Glass Canon cannot output that much additional damage all the time (limited use) or against all targets or more commonly has to take greater risks to use it, e.g. concentration with or without extra time. A flamethrower is often a poor weapon to run around in open war zones with its limited range and the tendency of opponent to explode the fuel tanks, but in those circumstances when it can be used effectively it's hard to beat. In a campaign where the standard is people use firearms, the flame thrower operator takes significant penalties, lower range, chance of being immolated by his own weapon, which help off set the advantages of energy damage over physical damage, area of effect, and higher damage (whether straight dice or through continuous etc.).
2. The Glass Canon is squishier than normal so has to spend more of their time taking cover or other defensive actions rather than pumping out damage. Or perhaps the Glass Canon has a unique vulnerability and/or susceptibility that the other characters don't have.
3. A combination of any of Concentration limitations, lower speed, lower OCV with the high DC attack to render the character's expected damage per Turn roughly equivalent to the campaign standard. You can also take into account "utility" damage like autofire, area of effect, range etc. A Browning M82 .50 sniper rifle hits harder bullet for bullet than an AR-15, but weigh 4 times more, and until contradicted by an actual sniper, a whole lot more difficult to fire accurately from the shoulder. The M82 might be a 4d6 RKA (Active Points 60) and an AR-15 is 2d6 RKA autofire 5x (Active Points 45). If you add OCV penalties for not shooting while braced and set to the M82, you probably have reasonable balance between the two weapons. The Sniper is stuck setting up and bracing, while the assault rifle is free to move and fire in a dynamic environment.
4. Additional damage can also be balanced by the campaign ethic. If, for example, producing corpses is a "bad idea" then those with extra damage are going to be further constrained from using high damage attacks/weapons with the "beam" or "always full power" limitation ('cause it's hard to pull a punch with a flame thrower).
5. Additional power that doesn't translate directly into damage may not need to be as vigorously monitored. Some powers in the source material end up costing an awful lot of points without really unbalancing the campaign. Most "subtle" mental powers fit this description as the extra +20 Ego effect to make the target unaware of the power tends to bloat the power beyond it's direct effectiveness on combat. So if you allow mental powers, as I have on occasion, you might allow "+7d6 [Mental Power] standard effect only for purposes of achieving +20 Ego for target unaware of attack" and not count that as part of the power's active point limit. A Mega scaled group teleport spell just to get the team from one part of the world to another may be rather expensive, but again it won't really unbalance combat nor will the other players feel bad about getting to the adventure that much quicker.