At the moment I keep a high amount of cash in my investment account. One might or might not debate the wisdom of that, but I mention it because I think that if you do desire to keep cash in your portfolio, you are BETTER OFF not using DITM leverage for long term stock holdings.

I would say that this is two separate holdings.
Cash has one characteristic, stocks have another, bonds have another, options have another.
Think about the reasons why you keep a high amount of cash.

The DITM LEAPS are essentially buying some leveraged BRK. Leverage costs money but you do it when you expect the stock to go up handsomely, much more than the leverage costs you. The thing about buying calls is that you can't lose more than you invested.

These options you are expecting about 2X leverage. If BRK goes up 10% the call is expected to go up 20%. The (implied) interest rate it costs you is not a separate thing like a margin loan, it is built into the option price.
It's not 5.21% vs. 4%. It's a price that is higher by the equivalent of 5.21% interest.
It's like when people buy an ETF with a high E/R, which they expect the ETF performance will be outstanding and more than cover the E/R.

1) is there a way to get better than 5.2% on cash with a term of about 2 years, which is the term of the BRK call I looked at?
No, not really. Current actual interest rate is about 4%. Anything more than that has additional risk.
However:
a) There are 3 year MYGA's that pay ~5.5%. 2 year a bit less.
b) BAC & WFC preferreds yield about 6%.
c) JAAA yield is 5.5%

2) Is there some other reason/value in holding the cash in one pile while having the implicit 5.21% loan I am paying for with the DITM call?
Yes.
a) You hold cash for a different reason than you invest is a stock or option.
b) The "implicit loan" is not really a loan. It is a fee. An entrance fee that you expect to be more than covered by the gain of the investment.

Up until recently you paid a fee (commission) to buy and sell a stock. Nobody treated this as an implied interest rate, even though it could be done so just like you do it on DITM options.

Important note: At the current metrics this is NOT the time to buy DITM calls on BRK.