> we could take the same view with other technologies like

Yes. We should look at fundamental physics when making investments.

Fusion is mostly dumb for almost all application. Most nuclear rocket engine designs are pointless and not really worth it as well.

> imho those people had been testing their technology for years but the company size and available cash is nowhere to be able to proceed with the desirable development speed

If you are proposing a design with limited upside but at least 100 the cost of a conventional design then of course you can't do that.

The reality is the Skylon project was barley more then 1950 sci-fi, to go 'full speed on development' would have cost most of the European space budget. And all for a concept that serious technical issues, a team with insufficient knowledge and experience and limited upside.