The short answer is that 'safer' is subjective and depends on your requirements.
You are both correct. Movement attracts the eye, so your blinking light is noticed. It is easier to judge the position of a steady state light.
For a motorist to pick out your tail light, particularly, from a sea of noise is very difficult. The surface area of the light is tiny, and it's all on its own. Your light is just not important enough to notice amongst the jumble of signs, traffic directions and other cars unless it does something to stand out, like flash.
My understanding is that the reason it's easy to see cars (apart from bulk) is that they have 2 lights moving together. Something to do with your brain automagically resolving the connected pattern. That's why it's hard to see a car with one working taillight, or a motorcycle or bicycle.
In terms of safety, my policy is always 'be seen and misjudged' rather than 'not seen'. So I always set both front and rear lights to blink at night. If you need illumination for the road, I'd strongly suggest a second forward light for that.
From Rear Lighting Configurations for Winter Maintenance Vehicles
Flashing lights will be perceived as having higher brightness than steady-burning lights, up to a flash frequency of about 15 flashes per second. Such brightness enhancement can aid in conspicuity, and several rear lighting systems have been designed to have a flash rate between 5 and 9 flashes per second in order to maximize their perceived brightness. While conspicuity may be greater with such configurations, an observer’s ability to make accurate judgements of relative speed or distance may be compromised when flashing or strobing lights are used. Croft observed that the judgments required in tracking an object were difficult to make under strobing conditions, yet very easy in steady-lighting conditions. Observations made during a study of service vehicle lighting for maintenance operations similarly pointed out that strobing and flashing systems designed for maximum conspicuity can at the same time reduce one's ability to judge relative speed and distance. Periodic sampling of the field of view in another study resulted in deterioration of one's motion-tracking ability that increased as the distance to the object of interest decreased.
Also from Selection and Application of Warning Lights on Roadway Operations Equipment
Flashes are bursts of light which, by definition, are unexpected
because they do not occur in nature (save for lightning).
This characteristic is their most important feature and
why they are so good at capturing attention.