Unfortunately still a widespread concept that tends to not make you a better climber in the long run.
Plastic isn‘t rock, you should rather train such aspects that make you a better climber overall. An example are positive holds that even hard rock problems have. Positivity is an indication of how easy it is to maintain contact with a hold. The more outward pull the hold can sustain, the more positive it is deemed. And there lies the problem since with enough finger power you can hold onto even a small positive hold though your body position is off!
For your technique it is better to train on flat surfaces that come into the wall at a 90 degree angle. Greater angles than 90 degrees are considered slopey and force you to move more precisely. Theme boulders, for example ”only pinches“ or ”my weaknesses“. Main training aspect for competition climbers. The principle of bouldering is preserved.
setting something that will force quality of movement as a criteria for success. For example ”statically impossible“ or ”dynamically impossible“. Like above, keyword being”working on my weaknesses“. Setting parcours like in Fontainebleau a homogeneous demand regarding the difficulty but varied with respect to the movements. Is now being offered by many bouldering gyms.
Shaping your own two square meters of bouldering space attractively
Don‘t use smaller handholds but smaller footholds. Try using only very small footholds with Spax-screws or even just the structures of the wall. Or a handhold is a foothold (also known as tracking). You may use only footholds that are handholds at the same time. Both are very good ways for developing body tension. Sit-starts, where hands and feet are already in position when the bottom leaves the ground as the last body part calling for power and flexibility!