Not sure why you think expensive, slow, networks incapable of accepting or transferring value would help store more value, much less be required to store value adequately, but that's your opinion I guess
I guess you consider safe store of value to be value not even you can access when you need it...
Store of value by definition means, you store and not liquidate very often. Either dont make it this tagline or deal with this question.
If its designed for store of value, it is not a highlight to say fast transactions. Which mean even if you had 10 min block, it would have served the purpose.
You imagination is slower speed is expensive, thats not how things work.