That's a good idea. Write to the Chancellor and suggest she abolishes tax concessions for ISAs.
I have a feeling your suggestion won't get much support,but by all means try it.
As a fallback, you could ask her to limit ISA value total per person. And Pension Fund value per person. Would a £million be too much? It seems more than generous to me.
p.s.
I don't approve of cash savings, so I haven't got much. I think I've usually got around £5,000 in the bank, and bills to pay within a month maybe around £2,000. If I'm holding cash beyond that I put it in Premium Bonds until needed, to save myself the effort of a tax return. I like to have a buffer in case I unexpectedly need a new boiler, or a roof repair or something