I As far as your spinning rod and reel problems I have never heard of such trouble with the bend in a spinning rod. The scientific fancy name for the bend in a rod is "Parabolic curve." Your Parabolic curve or bend should be an axis of no more than 50%. Some guys use rods so stiff they hardly bend at all, usually Bass Pros. If your rod bends as much as yours does that rod may have a break in the inner graphite.
One of the most understood things about fishing are rod ratings.
Blank designer use tapers, sometime multiple, hoop strengths (thickness) and materials (graphite, fiberglass and hybrids) to control where (action) and how much (power) a blank deflects under load. From there, it's up to the skill of the rod maker to design and build a rod to met the customer's expectations.
I keep no less than 10 blank manufacturers catalogs on-hand when selecting the right blank for a customer. More times than not, you can find a suitable blank off the shelf but there are times when the best you can do is get close, then modify accordingly. Trimming from the tip of a blank the rod makes them "faster". Trimming from the butt makes them "slower". You can affect a rod's action and power using guide selection and placement as well.
On spinning rods, I use "Concept" guides and placement exclusively unless asked otherwise. I got to chuckle when I see "Concept" rods sold in stores. How do you mass produce a rod where guide size and placement is determined by a reels up sweep (angle between spool and blank) and spool diameter? Yes, they do vary greatly even within single manufacturer's product line.
A spinning rod matched to the weight it says on the side of the rod as well as what test line you should use usually in Mono, there are charts available that will translate Mono to other types of line we have today.
Not sure how this would work. Tensile strength is tensile strength.
The line ratings do not indicate how much weight the rod will lift or suitable line weight directly. The rating on the rod indicates the most suitable breaking strength line to use on the rod, assuming the drag is set correctly (25-30%) on the reel. The rating is specifically designed to achieve a working curve in the rod, without reaching the rod's "lock-up" point.
To determine the "working strength" of a blank, run some line through the rod and attach a scale to the end of the line. Pull down on the scale until the rod has a good working curve. The weight on the scale gives you the drag setting for the reel.
Working out the line to use on the rod is simple. Multiply the working curve weight by four. For instance, if the working curve weight is #5, then you should be using #15 to #20 line with your drag set to #5.