You turn 50% of the time. That should get better with practice. Think about the centerline of your board as you move your feet for jibes. (The farther from the centerline, the more tippy). I ride a kite size smaller on a surfboard. This prevents you from being overpowered, and helps with the agility of a smaller faster kite. Try to keep your kite between 11 and 1 while jibing. Would you progress quicker on a different board? I believe that both of the boards you mentioned are too small for your weight. I would highly recommend a wider board if you want to progress faster. Both the Mitu 5'10" and Whip 5'4" are only 19" wide. At your weight, you may want to look at boards up to 23" wide. For length, you may want to keep it under 7'4". For strapless, don't narrow your search to kite specific boards.
I believe it was Felix Pivec who gave the good advice on riding the same size board that you would prone paddle surf. I call kitesurfing the lazy man's surfing. It is true that you don't need volume to kitesurf. But volume does affect the ride. In lulls, you will sink with less volume, which will require more force to get up to planning speed. With a low volume board, you will require kite power or pumping to maintain your planning speed. On the topic of light winds, a low aspect ratio board will get up to planning speed faster. As a surfboard gets longer, your nose is more likely to catch chop. A board with less rocker will get up to planning speed faster. A board with more surface area in the tail will get up to planning speed faster. So what type of surfboards are efficient and be good for light winds? Boards that come to mind are fishes, chop tops, grovelers. In my experience, the wider the board, the easier is it to learn on. If you revisit Felix's suggestion, what size of board should you be riding? At your weight, if you were a pro you would be riding a 29-33 L board. If you are an experienced advanced surfer (decade) you could be riding a 34-41L board. If you are an advanced surfer (< decade) you could be riding a 42-53L board. If you are an intermediate you could be riding a 54-66L board. If you are a beginning intermediate you could be riding a 67-81L board. With the power of a kite, which can act like a crutch, to allow you to ride a size board above your prone paddling ability. But the higher you go above your ability, the steeper will be the learning curve. Both of the boards you mentioned are too small for prone paddling, even for a pro at your weight (more suitable for a 73 kg pro). Once you go under the pro volume, any volume of the board does not help. You might as well be on an alaia, paipo, or skimboard. It sounds to me, like you desire a board to lessen your learning curve.
Thruster: A thruster has drag to help with tighter turns. For light winds, a twin fin set up is optimal. Add a quad for control at high speeds or holding on to a lot of power (overpowered) or steep waves. A 5 fin futures fin configuration is versatile.
Low volume boards are great for powered riding in choppy conditions where thin rails will slice through chop.
(volume to weight calculator) https://surfsimply.com/volume-to-weight-calculator/
(ranking your surfing skill level) https://surfsimply.com/what-level-surfer-are-you/