I’d say the best way to measure is by results. Are you scoring better against the same players than you did before? It is unlikely that all players at the club are steadily improving. Usually, especially when it’s all adults, most players’ level will be stagnant, so it can be a good measurement to see if you are scoring better against the same players than a year ago, or 5 years ago.
I think a racket’s balance is more of a personal preference separated from playing level. But as timing, technique, and power improves, a player can find that they can more easily access the benefits of a stiffer racket. In general, a flexible racket will be easier to play with, while a stiffer racket allows a higher power ceiling and perhaps a crisper feel. It is a similar effect to playing with a higher string tension.
Still, there are plenty high level players that play with flexible rackets. Stiffer rackets require more effort and precision in technique. Despite the benefits, due to the less forgiving nature of stiff rackets, it can lead to more mishits, mistakes, and loss of power when not hitting cleanly. At most levels it is more important to not make mistakes than it is to have a slightly better smash. Your preference for flexible rackets is likely due to the ease of use. This allows you to not worry too much about perfect technique and instead focus on tactics, your own game and the opponent instead.
If you improve and find that you are consistent enough with more demanding rackets then more power to you, but many decide that it is not worth the tradeoff. I remember Lee Yong Dae played with Bravesword 12 for quite a while, a famously forgiving racket.
I play with Apacs fusion speed 722. Very light, even balance, medium stiff. That is as stiff as I ever want it to be.
Finally, try to find a consistent partner. It is difficult to judge yourself on doubles play if you play with many different partners of varying skill levels. It is possible to adopt bad positional habits when playing with worse players, even if it improves your results with those players. It’s easier to judge a doubles pair than a doubles player, because it can be troublesome to determine whether you or your partner contributes to a win or a loss. Usually players are biased towards themselves. Therefore it is best to find a partner you enjoy playing with and practice together and judge yourselves together as a unit.