Not requiring some kind of theme for Multipowers is probably a problem with HERO.
Multi A, 60 point reserve
6u-12d6 EB
6u-4d6 RKA
6u- 8d6 EB Explosion
6u- 6d6 EB 5 shot Autofire
Our character can use lots of fire attacks. He's got 2 powerful blasts of fire, one killing - which is probably more appropriate for fire, but since it's supers game, he has the normal since you aren't supposed to kill everything. He can throw an AE fireball or swarms of little firebolts. The cost is 84 points.
Or you can have a multipower with an EB, +30" running for bursts of super speed, 60 points of strength with no figured, Telepathy, and say Healing for the same cost. If you can add any cool power for a mere 6 points, then there's not a good incentive not too. Of course, buying STR in a multipower isn't as cost effective since you lose the figured stats.
One thing about 5th ed is that it reccomends low defense values, at least compared to the guidelines for attack DCs. DCs are supposed to be from 6-14 - I've commonly seen 12 DCs or 60 AP as a common limit or guideline at the HERO boards - while the defense guideline is 20, with 10 resistant. All values are for "Standard" supers, aka 350 points. With 20 def, even an 8d6 attack will sneak some stun through and 12d6 shot will KO in 2 hits.
I also think that teamwork is very important. With Sweeps and Rapid Fire, it's easy to pound on someone with a low DCV. Using things like Flash, or Entagles that take no damage to cripple someone's DCV, and then having a partner drill them with a quick barrage of attacks seem like a very effective move, but requires different builds. The entangle would be pretty expensive, and the character would probably require a high speed and dex for shooting first, while the hammer probably needs rapid attack, high movement, good attacks and moderate CV. While nothing prevents a character from being able to do both, it would get expensive, and 2 people would be able to pull it off in the same segement or on back to back ones, so it's better split up.