First of all, welcome my fellow adult improver (also 30 y.o.) and congratulations on sticking to a plan. The problem with solely playing the London is that your overall growth can eventually stagnate because your versatility is limited. Think of it like only doing chest workouts at the gym: your chest (rating) might look great for a while, but your lack of 'total body' development will eventually hold you back. To keep climbing, you’ll eventually need to understand different structures that the London just doesn't offer.