Yeah, but Phasers would be made from superior synthetic materials (batteries too)... it stands to reason that weight wouldn't be a factor here.
A typical Type II phaser from say ST: Nemesis is small and very light... I don't think carrying 4 or 5 of them in one hand would be an issue weight-wise.
As for the central emitter not being used... maybe its not an emitter, but rather an exhaust vent for the heat... or its just that she didn't have to use it.
In all honesty, if a Type 3 phaser doesn't overload, then I doubt having 4 or 5 of Type 2's (or even 1's) rolled into one would present an issue... those things would be passively cooled... or basically, the excess heat (if any is produced) would be captured and harvested back into the power cells.
In fact, is there a reason to think Type I phasers couldn't vaporize people?
I don't think so... and we've seen how small a Type 1 is... (smaller even than Type 2)... so having 5 of those rolled into one seems perfectly doable.
We'll see, it's all based on people's preference.
I'm not too worried about heat, they usually figure that out at the design & engineering level.
It's more of a size, weight, ergonomics, & balance issue, but some people like big pistols, & others have liked heavier pistols.
So it's really personal preference at the end of the day.
As for Type 1's not being able to vaporize people?
Probably Battery Output limitations and it's stated that Type-1's had 1x Pre-Fire chamber to accumulate energy before release through the emitter crystal.
Type-2's had 4x Pre-Fire chambers linearly connected, right before the emitter crystal.
Type-1's had 8x power Settings while Type-2's had 16x power settings.
On Type-1's Setting 8 was the Maximum Power Output.
Type-1's are about the size of a modern day car alarm remote control.
Type-1's had power levels of (stun to up towards 1.55x10^6 Joules of energy discharge for 0.28 seconds) according to my TNG illustrated tech manual.
The EM Nuclear Disruption Force ratio was 1:40.
For reference, it would take 3.0 ×10^9 J of energy to totally vaporize a human body, including skeleton (break all atomic bonds). That's 717 kg of TNT to accomplish the same thing.
So assuming Type-1's Level 8 setting is the same as Type-2 Phaser's and Type-3 Phaser's.
At Level 8, factoring a 1:40 advantage multiplier due to the inherent nature of "Nadions" that you're firing upon the target, you would need to apply ~ 13.548 seconds of Level 8 energy to a target before it vaporizes.
Obviously if you increase the power settings on a Type-2 or Type-3 to level 16, you'll be able to emit more energy faster.
But that's the data I can scrounge up.