I guess this service might prevent people from migrating off Amazon services to DigitalOcean (or other VPS providers), but I don't really see a compelling reason to use this service instead of DigitalOcean.
Imagine if you could easily spin up DB instances and create LBs within LightSail - they would offer more features than DigitalOcean (or any other "VPS Provider"), while being price and usability competitive.
I would definitely be nervous if I was DigitalOcean - there are still advantages (support, tutorials, etc), but this closed the gap significantly.