An iframe embeds a separate document inside the operator page. Shadow DOM encapsulates a component's DOM and styles inside the same document. They solve different boundary problems and are not interchangeable definitions of “legacy” and “native.”
What an architecture review should compare
- Security and ownership: origin boundary, sandbox policy, content-security policy, credential and session handoff.
- Performance: real-user game-launch latency, transferred bytes, main-thread work, errors and recovery under representative devices and networks.
- Experience: responsive sizing, focus, accessibility, scrolling, theming and navigation behaviour.
- Data: consent-aware event definitions, postMessage or component API, deduplication and reconciliation with wallet/session records.
- Operations: provider update ownership, versioning, rollback, outage isolation and support responsibility.
Do not infer conversion from the label
An iframe can perform well or badly; the same is true of a component using Shadow DOM. Integration choice may affect load and continuity, but an uplift in registration, session length or revenue requires comparable traffic, a pre-defined rollout and downstream contribution-margin evidence.
Before selection, require a production-like demo and a measurement contract: eligible sessions, device and network mix, launch event, error states, abandonment window, consent treatment and exclusions. Choose the architecture that satisfies the exact security, UX and operational scope rather than the one with the stronger adjective.