365 has legal hold / eDiscovery which is akin to email archiving but better. In terms of proposition they can receive Business Basic for free, so Email, Teams, OneDrive / SharePoint, etc. SmarterMail cannot compete either with the free not-for-profit option or even the lower cost business packages. Charge to migrate them to make a few $$$ then charge them monthly to administer their tenancy.
Realistically the numbers for SmarterMail do not stack up when compared to what Microsoft or G Suite offer. Once you have factored in SmarterMail Licensing, Microsoft Licensing, Physical kit, colo/DC costs, management costs, support costs, backup / DR costs, etc, etc can you compete with commodity 50GB+ mailboxes for circa $5.
The situation is not specific to SmarterMail but email in general.
Great support is a selling point, it can certainly be attractive to clients but it comes at a cost to you which commodity priced mailboxes is unlikely to recover.
It would be interesting to know the thoughts of others, perhaps I am being too pessimistic today but given the thrust of Ron's question and experience perhaps not :-/