Playing alone taught me more than any coaching video.
My duo partner had surgery in February and was out for six weeks. I refused to stop playing so I ended up solo queuing more than I ever had. It was miserable and it made me better.
The first thing I noticed was how much I'd been relying on him to rotate. In solo, no one is rotating for you. If you double commit, you die. If you cheat up, you die. It forced me to actually watch the whole field instead of just my little corner of it.
The second thing was communication — or the total lack of it. Quick chats are a language and I got fluent. 'Take the shot!' at the right moment can turn a lost play. Silence at the wrong moment loses one.
Was my rank higher at the end of six weeks? Slightly. But my game IQ jumped a lot more than the number showed. When my duo came back we hit our peak inside a week.
If you've been playing with the same partner for a long time, try a solo weekend. You'll be uncomfortable. That's the point.