Build a customer segmentation that tells your team what to actually do differently for each group

Help me design a customer segmentation. The test I want you to hold every segment to: if this segment didn't exist, would the team behind it actually treat that group of customers any differently? A segmentation that's interesting to look at but doesn't change a single action isn't done yet.

BUSINESS GOAL FOR SEGMENTING
Reduce churn among mid-market accounts by targeting retention efforts where they'll have the most impact.

DATA AVAILABLE FOR SEGMENTATION
Monthly spend, tenure in months, product usage frequency (logins/week), support ticket count, plan tier.

WHO WILL ACT ON THESE SEGMENTS
The customer success team, who can assign a dedicated CSM, offer a training session, or flag an account for an executive check-in.

EXISTING SEGMENTATION IF ANY
Currently just split by plan tier (Basic/Pro/Enterprise), which the CS team says doesn't actually predict who's about to churn.

Do this:
1. Propose 3-5 candidate segments based on the available data and business goal, each defined precisely enough (specific thresholds, not vague labels like "high value") that a person could look at any customer record and assign them to exactly one segment without ambiguity.
2. For each candidate segment, state the specific different action the team named would take for that group versus another group — if you can't identify a concrete different action, cut the segment or merge it into a neighboring one rather than keeping it for descriptive completeness.
3. Check for segments that sound different but would actually contain almost entirely the same customers in practice given the data available (e.g., "high spend" and "long tenure" segments that are 90% overlapping in this business) — flag any such overlap and recommend collapsing them.
4. If an existing segmentation is already in use, explicitly compare your proposal against it and say whether it's worth the disruption of changing, or whether the existing one is fine and doesn't need replacing.

WHAT NOT TO DO
Do not propose a segmentation scheme purely because it's a common industry framework (RFM, personas, life-stage) unless it passes the different-action test above for this specific business — a well-known framework that doesn't change anyone's behavior here is still not worth shipping.

OUTPUT FORMAT
1. Segment definitions (precise, threshold-based), 3-5 total after merging
2. Action mapped to each segment, stated as what the named team does differently
3. Overlap check results and any recommended merges
4. Verdict on replacing the existing segmentation, if one exists, with a one-line reason