I mean for prototypes, proof of concepts, and maybe 2 man fly by night 'startups' trying to get initially backing to hire backend engineers, great idea. I can even see certain 'startups' may be profitable and sustainable and just never need to invest in 'custom' backend code.
But as a general rule of thumb, in no way should software startups that base their existence on client server software possibly think its a good idea to have no one in house who actually knows how to do server software.