Frothbewithyou
No, you can have preinfusion with a tanked machine, it uses the pump, just not at full power. If you have a machine that’s plumbed in then you can preinfuse using the mains water pressure without using the pump.
Plumbing in a machine is mostly a convenience thing, and doesn’t really link to features. Profiling machines can be plumbed or not, but there is no requirement. In the prosumer space plumbed only machines are quite rare. If plumbed in is offered it’s usually as an alternative but the machine has a tank too.
Dual boilers are always going to have better temperature control. The water is only trying to do one thing. It’s held at the temperature you need for brewing (plus a bit extra for the heat lost on the way to the group head). HX machines keep the boiler at a higher temperature as it’s needed for steaming. The water in the brew circuit stays at brewing temperature by continually circulating out to the group head where it cools down (known as a thermosyphen). When you brew you pump cold water through the heat exchanger where it is heated up to brewing temperature. It works fine, but it’s not as precise as the water flow rate will affect its temperature. Given you intend to mostly drink black coffee I wouldn’t go this route. Don’t forget most dual boilers let you turn off the steam boiler, so if you’re just making espresso you only need a hot brew boiler.
If my explanation makes no sense, then here’s a video with cutaway machines that shows how each technology works:
