No, not a 'juicer'. If you want juice, you need a juicer. That is an improvement having a stainless strainer for tomatoes and cooked apples for applesauce. Think 'babyfood' and tomato 'sauce'.
Your thinking is sensible but it will not give you clean liquid juice. Seems like alot of work to try and get juice from a few different appliances. You could experiment with your ninja to make healthy smoothies, some frozen fruits,(banana, blueberries) add a few greens like kale/spinach, frozen cherry tomatoes, a bit of plain greek yogurt.
A good juicer is the Breville all stainless. I got mine on Ebay, lightly used, half the retail
price. (a single guy that just did not want to bother with the shopping and cleaning)
I used an Acme juicer for years, just a bit of a mess to clean but not that bad. I like Carrot, beet, celery, ginger, apple,sometimes kale if i have it. I do not like a 'chewy' juice, so a juicer is necessary. A better quality blender is needed for really smooth 'smoothies' like a Vitamix or Blendtec. They will not extract 'juice'.