I don't know anyone with a fully pumped system that complains that their hot water cylinder runs out of hot water. They can be reheated in the time it takes a person to have a bath. However, the older gravity hot water systems suffered from this as they were slow to reheat the cylinder.
1. pipes everywhere in your bedroom cupboard.
With a combi extra pipes will be required in the kitchen (or wherever the combi is) instead of hidden in a airing cupboard. A non system heat only boiler can have has as few as three neat discreet pipes and a condensate drain. A combi will have those plus a cold water supply pipe, hot water supply to the taps plus isolation valves, filling loop and possibly a larger gas supply pipe.
Hypebole? There won't be controls everywhere. The user controls are a timeswitch and room thermostat the same as a combi. There will be a motorised valve & cylinder thermostat but having them outside of the boiler can be an advantage. See below.
Easily accessible for DIY replacement with readily available standard parts.
3. external control valves,
No need to call a Gas Safe engineer to open up the boiler if they fail, so great for DIY repairs using standard parts readily available from local plumbers merchant or DIY shed if it's a Sunday. With a combi, the comparable items (plus a quite a few extra) are inside, so it's a wait for the Gas Safe engineer to come with specialised manufacturers parts.
4. Loft filling and venting tanks gets contaminated with dust, and other debri, the hot water is not suitable for drinking
Not a problem with properly installed tanks with Water Bylaw 30 kit. Also keeps system topped up no need to repressurise the boiler at regular intervals or after bleeding or removing a radiator. Also easy to introduce corrosion inhibitor into the system.
5. very messy when it goes wrong, water could potentially leak upstairs and cause flooding and water gets in your ceiling, and electrical wiring.
Any system can leak. There's still a lot of water in a combi when it's connected to seven or eight radiators.
I'm not anti combi, they do have some advantages. They provide mains pressure hot water, they free up space a hot water cylinder would require (although you loose the immersion heater as a back up) and they are easier to install as part of a new system. Engineers like them as they don't need to employ the services of an electrician as most of the wiring is inside.