I suspect there's a hidden trap here due to survivorship bias - those of us who were lucky enough to see hugely successful products/services that got some of these decisions spot-on in the beginning, see how wonderful it can be when you are able to make these investments early on and build things once. The risk is that you fail to count the number of teams that did the same sort of analysis process and still made the wrong decision because they ended up pivoting, or just straight-up made the wrong call...
Replacing a managed solution in a small-scale product really isn't required, because it likely doesn't cost you enough. Replacing it in a high-scale product does matter, but that also mean you should be making enough money to make the replacement pay for itself.
If you make the decision to use the managed solution and it's wrong, that's something you can usually fix. If you go DIY when you should have paid for it - you rarely get to correct it in time, and it might just be another nail in your coffin due to lower velocity, focus, etc...
Replacing a managed solution in a small-scale product really isn't required, because it likely doesn't cost you enough. Replacing it in a high-scale product does matter, but that also mean you should be making enough money to make the replacement pay for itself. If you make the decision to use the managed solution and it's wrong, that's something you can usually fix. If you go DIY when you should have paid for it - you rarely get to correct it in time, and it might just be another nail in your coffin due to lower velocity, focus, etc...