Isn't some sort of bypass *required* in a cooling system? That was what i was taught.
Now, where that bypass dumps / the route it takes might make some difference:
On my Chevy, bypass is through the heater core only, and a hose goes from the intake, to the heater core, then to the radiator on the same tank as the lower radiator hose, only at the top. You shut off all flow through that heater core and bad things are a gonna happen.. Air temp is controlled by air doors in the heater box.
This is probably not optimal plumbing for quick warm-up, as it means the bypass coolant that normally should stay in the engine and heater core is getting to intermix significantly with the bulk coolant sitting in the radiator way before the thermostat opens. But, it may pay off by including the transmission cooler built into the radiator as part of the bypass loop. Dunno.. It would tend to smooth out temperature swings due to thermostat opening / closing a bit.
Older Chevys returned coolant to a nipple on or very close to the water pump intake. This would have much less intermix with the coolant in the radiator, which means faster warmup.
Other vehicles have dedicated bypass loops, or have a two-way heater control valve that shunts coolant flow to a bypass loop when you shut off coolant flow through the heater core.