Surely if you're trying to re-implement PostgreSQL, it's, to put it mildly, interesting (though even here there could be discussions - perhaps you just need a specific slice of functionality?). But for many, many other things, which are at worst a few man-weeks works - and sometimes man-hours, if you're sober with requirements - you could win with the other approach. If you're adding something external, just make sure you're serious about that - documentation, technology background vetting, training, all those things. Otherwise the opinion that "external solution produced by team bigger than ours" is better could be based on an illusion.