Well, as you're too young to drive, I assume you mean your parents Mondeo. But of course a 19 year old new driver is safer than a 17 year old driver. You DO mature a LOT between 17 and 19. Maybe not much in terms of 17 to 30, but you have to draw a line somewhere.
Their knowledge of cars would be greater, as they'd be exposed to them more, and be at an age they're likely to see how much energy is involved in moving 1.5 tons of metal around.
What has alcohol got to do with it? Lets stick to the age limit shall we. If buying alcohol was a problem then we'd have to raise the learning to drive age to about 100.
70hp = safer for new drivers than 136hp. Maybe not in the 'get out of danger' as the car won't accelerate, but it'll VASTLY reduce their chances of getting into an emergency in the first place. Ever seen someone mow through shoppers, killing them all because of a few second inattention on a skateboard? Slower = safer in the majority.
No protection? I think you'll find ALL modern cars are a lot safer than some older ones! Okay, a Ka is built out of tin foil, but modern cars are a lot better, especially since NCAP caused them to raise their game in certain areas (possibly to the detriment of untested aspects).
Weighing next to nothing? It's feckin' hard to find a car that weighs less than 1 ton! 1.3 tons plus is more like it...
So no, I don't think a silly rep-mobile is more safe for a new driver.
Mods ruled out by costs? Open your eyes laddie - look at all the twats in Vauxhalls with blue LEDs, unpainted bodykits, daft fake Recaros and printed carbon fibre filler flap covers. Ricing is alive and well (with a plus side that it means you can hear their fart-cans from a mile away, plus they make the car go slower, so you have more time to get out of the county).