Spending more time doing IN PATIENT is exactly what is going to better prepare you to be a hospitalist because that is what you do, take care of adult patients IN the hospital.
IM residencies will require more ICU time than FM. Placing central lines is largely not something that is required of a hospitalist anywhere. An ICU is simply one more kind of nursing floor where you can place a patient, if you have an open ICU you keep there what you think you can handle and transfer out what you cannot.
People can learn and pick up a lot after training. The overarching point here in this thread is that IF your goal is hospitalist medicine and your choice is IM vs FM, the choice is simple, and why waste your time learning a craft (pediatrics and obstetrics plus lots of outpatient clinic) you are not planning to use when done?
My anecdotal experience is that for many years after training FM trained hospitalists are simply not as good - they are not killing people or anything, they are adequate - and are much more uncomfortable with the sick and the complicated (they seem to find some parity after 3-5 years). This also does bias my opinion in the direction of recommending IM for someone interested in doing hospitalist medicine.
I really cannot change my recommendation because you can come up with a hypothetical scenario where an FM trained person will be better than an IM trained person starting a hospitalist jobs. I'm sure it can and does happen. It's not, however, enough to persuade me that those situations are occurring so often or at equal enough rates that FM is just and fine as IM.
This isn't personal, nor me taking a crap on FM.