Hi, I play freeroll, micro, low, and high stakes poker. In my opinion, each stake has a different level of players. And my honest answer to your question is whether freerolls or micros will help improve your game. Yes, it will help you learn how to play poker and experience different types of variance, but it will not help you improve your skills if you have a plan to play at a higher level. If you can call an A high or a bottom pair like deuces against someone who shoves a value bet or bluffs against your whole stack, then go play in mid-stakes or any upper stakes. I'm not saying micro-low and freeroll players are not good. Most who play at that level have long-term goals and correct their expectations with their day-to-day goals. But if you really want to learn and improve your skills at some crazy level, you must go up against players who play in the low-mid-high stakes; most of them don't play the cards; they play poker against themselves and your mind. It's hard to describe the actual feelings and the roller coaster of emotions that you will encounter.
So my point is, most players in the micro that you will encounter will shove all in with A high and some pockets pre-flop since the stakes are affordable and they could just re-buy all the time, while in the upper level you really need to maximize your time bank by thinking and evaluating if your decision is correct and what your next action is after your raise pre-flop.
This is my only opinion and perspective on how I see the different types of players on each level.
ADDENDUM:
You can read and watch all the learning materials available online, and they will help you gain a proper mindset but not your gameplay. People who wrote those lessons shared their 80% of strategies to help our game, but it doesn't always work like that. Those successful players only share 70–80% of their skills, not the actual 100%. And those lessons are very effective, especially for them, but that doesn't mean that they're also effective if you apply all of them. Just pick some good strategies that suit your style and apply them through trial and error.