There is one thing that I think can help with the sql overhead you mention - if you have a rock star dedicated sql person that can take all this work off your hands (that's not me btw, i've just worked/am working with such people). I think it affords you easier long term growth if you have expectations of making it to the medium to large company world, while not slowing you down when you are small, so I think it's a better strategy for both small and large companies. Are you signing on for a potential bottle neck? Yea it is a trade off and it is paramount you hire well in that area, but that's the sort of problems and decisions you have make all the time at a company.
I understand where you're coming from and what you describe may be workable in a smaller company with 7-14 devs where everyone knows what they are doing and understands well what happens under the hood. I think it's less likely to work at a company with 50+ devs though where you inevitably start trusting people less, or just at a company where you don't trust everyone. I've worked at both types. There is also the question of the complexity of your data and the way you need to query it. Right now we do essentially a ton of graph queries that we optimize highly in sql (ends up working much faster than any graph database since the schema and the queries are optimized for the exact data we are working on). Some of the functions that I write for this would not be implementable in an orm. I suppose that could be the case where you drop down into raw sql, but that happens to be a fair chunk of our code.
Maybe you can make it work better than I'm expecting, but if you were starting from scratch would you really want to go down that path anyway, all things considered? My original argument was that you are better off choosing a different way. I suppose that point of view will be difficult to change for me :).
I've used ORMs before i worked at myspace. NHibernate specifically. I've also used sql alchemy on the python side. NHibernate was in a professional environment, sql alchemy was a bunch of stuff I did for evaluation purposes, so you can discount that if you like.
And i'm not working at a data warehouse.. why do you think that?