You are correct that SDAs spend money on all sorts of things JWs don’t spend money on such as schools and hospitals.
On the other hand the vast majority of SDA membership and institutions are in third world countries.
Plus a church can only spend what it receives. The SDA church receives on average $178 from each of its members. (20 million members)
Indications from the paperwork in the UK and Australia are that JWs in those countries contribute in the region of £200 to £300 per year. If we assume that JWs on average contribute £200 a year that comes to £1.6 billion which must be pretty close to $2 billion dollars.
And since $2 billion is a reasonable ballpark estimate of Watchtower income it must also be reasonable estimate of their expenditure, or worse, since “more money is going out than coming in”.