DAQ systems can make very functional low-speed oscilloscopes, with a number of caveats:
Anyways, if you have a situation where you have fixed or low voltages, and don't mind doing a bunch of work on the PC end, a DAQ could be used as rather pokey oscilloscope.
They're really different tools, though, and while they do share some characteristics, they have very different intended uses, and this tends to show in their approach and the software design considerations.
It's also worth noting that most DAQ systems are designed for continuous, rather then triggered data acquisition. This means you're maximum sample rate is largely limited by the interface the DAQ uses.
For example, USB2 only has 480 Mbps(more like 400 Mbps real-world) bandwidth. As such the best sample rate that could ever be achieved would be 50 Msps(million samples per second) at 8 bits resolution, and very few implementations will even approach that. Somewhere in the range of 1-10 Msps at 8 or 16 bits is more realistic. Extracting all the available bandwidth from USB is very challenging.
Another consideration is what you're going to do with all the data. 1 Msps is a lot of data. If the 1 Msps stream is 16 bits, that's 2 Megabytes of data per second, or a gigabyte every 8 minutes. I don't know what you're intending to do with this pseudo-oscilloscope, but you can't just take samples willy-nilly, unless you're just displaying them and then immediately discarding them.
I've actually written a minimal real-time visualization tool for some IOtech-branded DAQ systems at work. It's kind of an oscilloscope. It works well, but I've also designed all the PCBs that interface with the DAQ system, so I could design them to work to the DAQ system's input specifications.
USB 3.0 runs the extra lanes at 5Gbps, which equates to a clock of 2.5GHz. So you will probably need at least 3GHz bandwidth, at an absolute minimum. Quite pricey! To see anything clearly, you'll want even more bandwidth as the signals have multiple harmonics - you would need at least the 3rd at 7.5GHz and preferably the 5th harmonic at 12.5GHz to see anything even remotely square.
But the thing that people forget is, a scope is only as good as the probes that it connects to. So not only do you need a scope with enough bandwidth, but also a probe which has the bandwidth too. The signals are also differential, so a differential probe is likely to be required.
At high frequencies like USB 3.0 runs at, electrical signals in wires are basically EM waves trapped in a waveguide (the cable). These signals are incredibly sensitive to impedance mismatches, so sticking any old probe with a long cable on it is just going to distort the signals.
You would need a probe which has very low capacitance and connected to the signals with as short of a run of extra cable as possible. Keeping the cable short essentially calls for an active differential probe. Expect such a probe to be in the region of $7k+ just on its own!
Best Answer
The 1970's is long before I started engineering work, but at that time an oscilloscope that measured beyond 100 MHz (maybe even 10 MHz) would have been quite an expensive instrument if it was available at all. So oscilloscopes were rarely used for RF work.
Furthermore, 1970's oscilloscopes were entirely analog instruments, and would provide you no assistance in estimating the phase of a signal. Your ability to do this measurement with a 'scope would be limited to your ability to 'eyeball' the phase based on the position of the traces on the screen (probably using an XY trace and estimating the aspect ratio of the ellipse formed on the screen). Maybe you could achieve 10 degrees precision with this method (and the precision and accuracy would depend on the experience of the operator doing the measurement).
Nowadays, oscilloscopes for RF frequencies remain relatively expensive, so you'd still likely use a network analyzer (one component of which is essentially an automated vector voltmeter) to do that measurement, if you were dedicating an instrument to doing it every day (for example, on a production line).