As the other person said, you can only duo with people within 1 tier of your rank (which is treated to be silver for first time ranked people), so bronze-gold. The duoing thing basically requires smurfs who have dodged matches to avoid being promoted past gold, and isn't intended as something you should do, just an explanation for how sometimes you see streamers place really high. Those players are almost always diamond+ though, so will usually be able to hard carry all their matches against gold/plats for an assured 10-0.
I strongly recommend you just solo everything though, at least until you have a solid understanding of what your skill level is. You referred to playing with gold/plat/diamond as being thrown to the "wolves" which makes me think you aren't comfortable playing at a diamond+ level, so you shouldn't be aiming make your placement matches harder.
If you're going solo and just stomping your way through placements and you're like 7-0, then yeah you're probably gold+ material and maybe you would've saved some time by duoing with higher mmr players, but if you're really doing ranked for the first time that is very unrealistic, and you should expect to place mid silver or even high bronze.