I have both. The Mini 5 Pro is superior but probably not “vastly superior”.
It’s more stable in the wind, it has a higher top speed, the camera is better (it has better low-light performance and a usable “lossless” 2x zoom) and the obstacle avoidance is better (with front-facing LIDAR). The free panorama mode is also genuinely useful to me, although I haven’t really found any use for the fancy rotating gimbal.
Whether the Mini 5 Pro is £200+ better, would be up for debate and depends on how much you need/want the upgrades. The Mini 4 Pro is a fantastic drone and has most of the features. Most of the improvements are incremental.
One other point to make is that the Mini 4 Pro is sold as sub-250g, whereas the Mini 5 Pro is not. That can have a slight impact on how easy it is to fly it abroad (e.g. Canada, the US). It has less of an impact in the UK and the EU though as both drones are C0-marked so they can both fly in the least-restricted A1 subcategory (i.e. over people).