but now that conservative movements have been co-opted by the alt-right

All that's really saying is the conservative groups have changed to something else. There are a lot of right-wing powers out there which are far more accelerationist than progressive left, want things to change rapidly. This just isn't conservative by definition.

As you described, older people want to protect the status quo - they are, philosophically & politically speaking, becoming more conservative regardless of who starts taking over the labelled entities.

maintaining the status quo really isn't sustainable,

This is true. There's certainly something to be said for those people who point out that it was because of our conservative complacency that we got in this mess to begin with. Putting our heads in the sand, and enjoying life as it secretly and invisibly degrades all around us. Not a concern however, something for future generations to worry about!

at least 5 roughly equally sized parties

Proportional representation pretty much. The problem is that it's about as far the other end of the spectrum as a dictatorship. Say of China what you will but a single party nation can get things done fast. A government of 5 parties generally ends up completely stuck, change is gruellingly slow and ineffective.

I think the UK has a bit of an advantage here compared to EU countries - if only we can get a solid party in power with a solid majority, they can essentially do a 5 year dictatorship approved by the voters, or even infinite years if the voters remain happy.

We actually see this with Labour. Keir Starmer, for all his faults, is getting tonnes done in rapid time. The only reason it didn't happen the last time the leaders had a big majority is because the Conservatives had constant civil war, insider backstabbing, crawling for power.

A previous majority, Tony Blaire, did much the same, an almost infinite number of new laws and regulations, complete transformation of the actual government's inner workings, and more.

Edit: Sorry, didn't realise I wrote so much for a comment!