You lot could always look at the JGSDF, they generate alot of units with a minimal manning level, but they don't have to worry about commitments all over the world either.I think you've quoted Division liability rather than Brigade
Whether a matching division would be possible in an army of 50 - 60K i dont know- a simple fantasy orbat on a basic numbers count would suggest yes - but reality is never so accommodating
That US Division will have additional Corps and Army level support as well such as tank transporter regiments, 3rdline engineering, strategic communications - Likewise A British Division would also need to be supported by those as well and as in industry theres a minimum size overhead you need to function. The smaller the force / business / whatever the proportionally larger the liability.
So for example it could be you need 30000 men in unavoidable support / Admin / training roles - in an army of 50K yet only 35000 in an army of 150K