The transformative integration of Machine Learning (ML) for Artificial General Intelligence (AGI)-enhanced clinical imaging diagnostics, is itself in development. In brain tumor pathologies, magnetic resonance imaging (MRI) is a critical step that impacts the decision for invasive surgery, yet expert MRI tumor typing is inconsistent and misdiagnosis can reach levels as high as 85%. Current state-of-the-art (SOTA) ML brain tumor models struggle with data overfitting and susceptibility to shortcut learning, further exacerbated in large-sized models with many tunable parameters. In a comparison with multiple SOTA models, our deep ML brain tumor diagnostics model, SIENNA, surpassed limitations in four key areas of prioritized minimal data preprocessing, an optimized architecture that reduces shortcut learning and overfitting, integrated inductive cross-validation method for generalizability, and smaller neural architecture. SIENNA is applicable across MRI machines and 1.5 and 3.0 Tesla, and achieves high average accuracies on clinical DICOM MRI data across three-way classification: 92% (non-tumor), 91% (GBM), and 93% (MET) with retained high F1 and AUROC values for limited false positives/negatives. SIENNA is a lightweight clinical-ready AGI framework compatible with future multimodal expanded data integration.