I used a 'Blad back in the seventies and never was able to hand hold for slow exposures; it replaced a Bronica S2a with a stovepipe which I could hand hold to 1/15 every time and 1/8 usually.
The 'Blad was replaced with a Pentax 6x7 which I could hold well with some lenses and not others. It has been 'supplemented' in recent years with a Mamiya 7 which, even though I'm getting old & shaky, can be held consistently at 1/15 using the normal lens. using both hands AND placing against the face gives three points of solid contact.
With any camera, practice your breathing when making long exposures. If a TLR, you must shoot between heartbeats like a shooter.
More than you wanted to know,
Russ