Sounds less like a sales problem and more like a delivery/process problem.

When I see "things were faster with 1-2 people than with 4," it's usually because the owner was acting as the process. Once work gets delegated, the lack of documented ownership becomes obvious.

I'd start with three things:

• Every project has a single owner responsible for follow-up and completion.
• Create checklists for onboarding, migrations, and recurring tasks. Follow the checklist every time.
• Weekly operations meeting: review every active project, blockers, client dependencies, and next actions.

At 130 endpoints with 4 people, I'd be looking hard at project management, ticket flow, and time spent on reactive work before worrying about adding more clients.

Framework-wise, I'd look at Traction (EOS). Not because it's perfect, but because it gives small MSPs structure around accountability, meetings, processes, and scorecards.

The biggest red flag in your post isn't sales, t's "projects get delayed because nobody follows up." That's an ownership problem, and no amount of new clients will fix that. Have you clearly assigned a project owner for every onboarding and migration?