It depends on how much time and money the player has. When you say it depends on the player, that's what you're referring to. If you have no time and money, you could play this game for 3 years and still barely make progress. If you have a lot of time, but no money, you can make significant progress in only a year. But if you have time and money, you can become an expert in a few months. You'll have diamond characters, catalysts, and moves that can get you into the diamond ranks of rift. No "strength" required.
If rift used a set score for the rewards, then you'd be correct, but because they use a percentage based approach (top 1% is diamond 4, etc) it doesn't matter how strong or weak you are in the game, it's all about how far you've progressed, which happens SIGNIFICANTLY faster if you pay, or have the time to burn.
All that said, it is still technically possible to reach the top ranks without spending money. It's just going to take you a really long time.