That is what I love about us guitar players, always so quick with a well formed opinion when it comes to gear, what you can and can't use for a particular sound.
Truth is you can play metal with any electric, heaven forbid even a Telecaster should you wish :)
You can do anything with a Strat, they are the most versatile of them all in the right hands. It may not surprise you to learn I have 2 Player Strats, an MIJ Squier and a Partscaster I put together. In saying that I've an SG, ES335, LP Traditional and a Jackson JS32 so I've plenty of experience using different styles of guitars with varying PUs and custom wiring.
If you are using a traditional style Strat SSS set up then at high volume, high gain or with a cranked up overdrive/distortion pedal you are going to run into feedback and unwanted noise that can be hard to control particularly on the bridge PU. The trouble is the bridge/middle and middle/neck can get muddy with a lot of dirt and/or high gain. The middle or neck aren't ideal for metal either and suffer from hum nearly as bad as the bridge.
Player Strats, infact I believe most modern variations tend to come with AlnicoV PUs which mitigate the problem compared to say older Squiers or some older Strats but I think the best thing about them nowadays is the way they have been wiring the bridge PU through the tone control which they never used to do. Just being able to roll off some of that shrillness you can get with cranked up bridge SC makes so much difference.
Copper foil shielding your Strat as well as just making sure it's wired well, good solid solder joints, decent pots, caps, wires, particularly that it's properly earthed at the trem claw and bridge. Taken all together can do a lot to cut out the less desirable noise a single coil strat can produce.
Cranked up a Strat will be more noisy than the average guitar with two HBs but in many ways if you can harness that extra noise, the kind of high output, barely controlled, contained feedback that is intrinsic to single coils and strats then it makes for a glorious, exciting, thrilling tone that's hard to beat.
It also depends on what you mean by metal, if you want a very specific tone then it. may be easier to go the HB route but if you want a raw, energetic, less refined sound which can suite certain forms of metal to a tee then the Strat is the way.