Process supervision improves perceptual grounding in RLVR-trained vision-language models, but it also incurs repeated verifier queries and reshapes the policy by suppressing exploratory entropy. We show that its benefit and cost are empirically separable: grounding gains emerge early, whereas the exploration cost accumulates with continued supervision, holding the policy’s entropy below that of outcome-only RLVR. This hidden behavioral cost shows up as skill tradeoffs on static benchmarks and, more importantly, as a degraded initialization for subsequent outcome-only RLVR that prematurely limits its reachable ceiling. Motivated by this asymmetry, we propose warmup-and-merge: early-stop the process-supervised warmup, merge only a low-rank component of the warmup task vector into the base model, and continue with outcome-only RLVR under an adaptive on-policy reward that targets the model’s current perceptual failures. Across multiple benchmarks and backbones, our method improves perception while preserving exploration, achieving stronger final performance at a fraction of the verifier cost of continuous process supervision.