Background/Objectives: This study evaluated neoadjuvant disitamab vedotin plus programmed cell death protein 1 (PD-1) blockade and associations of post-treatment neutrophil-to-lymphocyte ratio (NLR) and systemic immune-inflammation index (SII) with response and progression-free survival (PFS) in muscle-invasive bladder cancer. Methods: This single-center retrospective cohort included 71 patients with cT2–T3N0M0, human epidermal growth factor receptor 2 (HER2)-expressing disease treated between September 2021 and October 2025. Logistic regression and receiver operating characteristic analyses evaluated response endpoints; Kaplan–Meier and Cox methods evaluated PFS. Benjamini–Hochberg correction was applied separately to response analyses. Results: Complete response (CR), objective response, and disease control rates were 66.2%, 84.5%, and 88.7%. Of 47 CRs, 5 were cystectomy-confirmed pathological CR (pCR) and 42 were clinical CR (cCR). Response associations did not remain significant after correction (minimum q = 0.082). AUCs were 0.659–0.708. In a two-variable Cox model based on 14 PFS events, treatment cycles (HR 0.615, 95% CI 0.419–0.903; p = 0.013) and SII per 100 units (HR 1.205, 95% CI 1.073–1.355; p = 0.002) were associated with PFS, but these estimates require cautious interpretation. Two deaths occurred. Conclusions: Neoadjuvant disitamab vedotin plus PD-1 blockade showed promising antitumor activity. The pooled CR endpoint may overestimate pathological response and is not directly comparable with cystectomy-confirmed pCR. Without standardized pretreatment NLR and SII measurements, reverse causality cannot be excluded. Response associations and PFS findings based on 14 events require cautious interpretation and prospective validation.