The problem is, the word 'cancer' is an umbrella term for dozens of very different, and very specific diseases, in a similar way we say 'viral infection'. Viral infection can mean cold, flu, COVID, AIDS, meningitis, diarrhoea, smallpox, hepatitis, herpes, and so many other diseases, many of which have long been easily curable. Cancer is in many ways similar -- there are quite many which have long ago stopped being terminal and can be mitigated with modern medical intervention.We've spent gobs on cancer research for decades and had many, many glimmers of hope. And, in fact, progress has been steady and very worthwhile. But, no single silver bullet.
On the matter of battery electric flight, two components are needed: reliable and efficient motor, and reliable, efficient (and lightweight) energy storage. Motors are already there; they have in fact always been far more efficient (and far more less heavy) than comparable ICE engines. The only critical component is energy storage, and all those gobs of money and research being spent on battery storage seems to be steadily bearing fruit. For the past 20 years, electric storage technology has been steadily improving, roughly doubling every 5 - 7 years. We have almost hit the wall with the current chemistry (based on lithium), but there are other things on the horizon. There will certainly come a day for homebuilders when it will be feasible to build an RV10 and have enough battery capacity to fly it for 5 - 6 hours (and to re-charge in less than one hour afterwards).