The point of finding a racket and string combo that works for you is to give money to racket companies.
Pro players, if given the choice, will stick to what they're used to, which is what they grew up with (or something very similar). Sometimes, they are forced to change (when they switch sponsors). They'll tend to gravitate towards something closer to what they are used to. If there exists a racket that wows them, they need to commit to an adaptation period, which some are willing to go through. Federer noticeably went through such a period in 2014 where his strokes visibly looked uncomfortable with regard to ball control, but most of that discomfort seemed to go away within a year. Not many people are willing to relearn their strokes with the uncertain possibility of getting better or worse overall when they can simply look to stick with the same racket and simply improve themselves.
People that over-obsess on technique and equipment tend to go in circles. X improved with A change, but Y got worse, but I prefer X being better, so I'll stick with it. B improves Y at the cost of Z, new switch made. C improves Z at the cost of X, ah damn right back to the start. I could've just spent my time and focus improving X, Y, and Z independent of my equipment and technique.
tl;dr it's not the racket, or the strings, it's you. Changing the racket and strings are a temporary solution. In the end, you're going to have to choose between playing tennis for the rest of your life, even if it's not how you want to play, or playing the tennis you want for a VERY short amount of time before quitting the sport indefinitely.
However, the lucky bit for you is it seems the issue is your first serve? You can just use your second serve twice!