devtrackers.gg
Windows CPU usage is a bit misleading on multi-core systems, i.e. all of them nowadays. It reports TOTAL usage. So if you have, for example, a 4 core system, then "50% usage" means 50% of the CPU's total throughput is being used. That could be either all 4 cores running at half speed, or it could be 2 of those cores running flat out as hard as they can. Warframe tends to do the latter thing: It will typically run 2 threads as hard as possible. If those individual cores running those threads cannot keep up, then the game becomes CPU-bottlenecked even though there are other, unoccupied cores which aren't doing any work.
This is *further* complicated by the fact that modern computers will usually try to move highly demanding threads around to different physical CPU cores, in an effort to spread the heat around. So it runs on core 0 for a little bit, that core gets hot, the operating system moves the thread over to core 2 instead. The problem is that this "hopping" is happening much faster than Task Manager's polling interval. So what looks like 2 CPU cores with half usage, can actually be 1 single thread that's being bounced between them really fast and, again, hitting a bottleneck.
Typically a really easy way to tell if your computer is being limited by CPU or GPU performance, is to look straight up into the sky or straight at a wall where there's nothing behind it. This takes all the load off the GPU. If your frame rate goes up by a ton, then it was the GPU slowing you down, while if stays the same, it's your processor that is the bottleneck.
For laptops, typically the best things to do to improve performance are making sure your cooling is working to best effect (make sure all air intakes/exhausts are clear and that the visible grills/heatsinks aren't full of dust bunnies), and make sure you are plugged into the wall with "High Performance" mode set.