I'm going to be contrarian here. IMO the scissors jack is adequate and safe for a roadside wheel change,
as long as you are on firm ground and/or put it on a suitable slab or piece of wood. And don't change the wheel during an earthquake >M5.5.
I don't think the weight of the van comes into it provided you use a properly rated jack (as supplied). The weight of the vehicle is not a factor in how (un)/stable it is.
I was always taught to put the spare wheel under the sill so if the jack did slip you'll do minimal/no damage (then replace it with the removed wheel for the second part of the operation).
I'd
never use the scissors for anything involving work underneath the van, but that doesn't arise in just changing a wheel. For anything involving crawling underneath I'd not be happy with anything less than axle stands or ramps.
Unfortunately I guess people just don't expect to change wheels on cars/vans these days, I think a lot of folks have probably never even done it, and the very basic skills involved have been lost. So we collectively end up paying, indirectly, through higher AA/RAC (etc) fees so a professional can do it. Hurrumph.
But the last couple of times that I've had to call out recovery for anything, it's taken 60-90 mins for them to show up. So personally I'd much rather change the wheel myself - about a 15 min job and then on my way.