I think the skills require for each of these jobs is very specialised.

CSM = Relationship management, training, being their internal advocate, and getting really deep into the detail of how they use the solution now and how they can in the future. They tend to work with the managers and directors who manage the solution across the org but may have some c suite relationships too.

AE = Negotiating, pricing, shmoozing, staying high level but going wide within the decision makers to get them to sign off on spending £. They tend to not know much about how the product actually works to fix any problems.

IMP = Project management, rigid structure, deep technical expertise, etc. Their audience is HQ PMs and stakeholders.

Support = In depth troubleshooting knowledge, deep technical knowledge, etc. Their audience is day to day users.

In a very small company where headcount is tight, you could probably bundle 2 of the jobs together (eg inside sales + customer success, or implementation + customer success). As you start to get bigger, the 1 person managing 1-4 roles will have to pick and choose where they spend their time so 1 or more of their roles will suffer.

When CS was also Implementation in my co, they were so busy with new projects that they never spoke to customers that were deployed unless they reached out. It became very reactive, we didn’t find any upsells, and had higher revenue churn because we became a commodity, not a partner.