The answer is: Depends!
The real question is, would you want to play:
(a) The niche game (the internal team will provide consulting services and handle specialised requirements and overall coordination, while most generic and some specific needs will be outsourced) or
(b) The volume game (the internal team will take care of all the bulk training needs and overall coordination, while niche needs including analysis and measurement of those needs will be outsourced)?
There is no correct answer to this question - each organisation needs to find its own answer. Some of the decision parameters are given below:
1. What is your organisation's mandate for the internal L&D team size? What is your organisation's mandated L&D budget?
2. Are the right kind of resources available in your market at the price you can afford to pay, particularly for certain niche skills?
3. Can you groom your internal team to become not only great trainers but also effective consultants?
There are both types of outsourced vendors - those that play the volume game, and those that play the niche game. Also usually outsourced vendors do a better job of resource utilisation and consequently work out cheaper overall.
However the challenge is to find a few vendors that can integrate deeply with your organisation and pace with its changing needs, while maintaining consistent quality. These vendors should be able to deliver operational excellence in respect of the bulk requirements, and also have specialist credibility for catering to the senior and specialised levels. Such vendors are very few. Consider: how many vendors exist today who can credibly offer end-to-end training solutions for an organisation with national presence?
My preferred path would be, to view the Learning function as an independent business unit providing four inter-dependent but distinct services: Consulting, Training Operations, Training Delivery and Content Development. Keeping quality paramount, I would analyse the case to outsource or retain each and work out an appropriate mix for my organisation. And in all possibility, this mix will constantly change as availability of resources varies.