It's an engineering tradeoff and market adaptation.

If you are a typical SaaS provider the complexity may be beyond your capabilities and budgets.. allegory to a local delivery business choosing to build a long term relationship with a single vehicle manufacturer and dealer.

If you are a high stakes service provider, you need to start thinking about how to get out from being controlled by a single vendor and market flux and plot your own destiny.. allegory to a national shipping carrier sourcing vehicles from multiple manufacturers and developing long term relationships with them to refine the platform.

3-4 would be great. What would you pick for the rest in this day and age though?

Because tradeoffs and diminishing returns are a thing? For example having one backup is better than having no backups. Backups spread across earth, moon and mars would be better but probaboy not worth the cost.