IMO Vendor lock in is when you ask your boss why cant we use tool NEWTHING? Then they tell you its because they have a 5 year contract with Oracle/MS/IBM/Salesforce and that is what we are going to use. We aren't going to have 10 platforms.
Which means in 10 years they will really be locked in because no one is going to un-entrench that thing.
if you've made it to 10 years, that's a really nice problem to have (or maybe a really boring problem to have). But if you're just starting out, I want to prevent you from making all those decisions when you could really be focusing on your startup instead.
So I'm trying to encourage you to consider picking a platform and just sticking with the tools of the platform rather than bundling it yourself together.
Or like how atlassian suddenly started charging a "serverless event" fee for their various workflow automation tasks a couple years ago basically slapping a $5-$10k markup on a product you already own. Thats just for small companies I'm sure there are enterprise customers that are paying six figures for a previously free feature and shrug it off. Like you said a good problem to have.
It's still a good idea to abstract away these services behind a standardized interface. This way switching from one service to another is just a matter of providing an alternative implementation to said interface.
Granted this approach requires a little foresight...something many companies seem to not have nowadays.
Abstractions are not free either, so if you are creating this "standardized interface", the complexity price you pay is better be worth it.
Often it's less effort to lean in and use all features of the service than to limit yourself to a least common denominator between all competing services.
Which means in 10 years they will really be locked in because no one is going to un-entrench that thing.