I think the OP is quite right about motorists getting complacent. I think we all do from time to time.
I see it in drivers, pedestrians, cyclists and motorcyclists. Nonetheless, I quite like the current system. It seems to work reasonably well.
I've been hurling my children onto bicycles and encouraging them to ride along sweeping, fast, rural A-Roads since they were tag-along age. They were out there in rain, shine and sleet.
They are now 12, 15 and 18 and all remain extant. All still ride for pleasure on those very same roads.
These roads are populated by vehicles of between one and forty-ish tonnes, travelling at between 50 and 90 mph with only a human being in charge of speed, direction and road position. Human frailty being what it is, I think that as a wider road-using community we do OK.
I am regularly staggered not by the carnage on UK roads, but by how few incidents and collisions there are in a system of shared-use infrastructure that would never get off the back of an envelope if designed from scratch today.
I've been bumped off my bicycle many times and absolutely walloped for six in car and on motorbike... but I glory in the barminess of it.
One test at seventeen* and then only money and good sense stand between you and 500 bhp. That's part of the romance of life, isn't it?
Even better, cyclists can propel themselves into that Rollerball nightmare without even passing a test or an assessment.
(* I refer to the test in place when I was 17)