I agree with the entire post except this point...
(b) Has a decent amount of credit available (let's say $10k) in any form - credit cards are fine;
I don't agree that available (unsecured) credit is quite comparable to an actual e-fund, because the accessibility of the credit line can be canceled 1) if you lose your job and your creditors get wind of this somehow or 2) if your creditor runs into real fiscal trouble and ends up filing bankruptcy themselves.
Since #1 is one of the most likely scenarios wherein an e-fund would prove useful, it's not entirely a substitute for a well funded e-fund; but seems reasonable as a supplement for a bit-too-small e-fund and/or paired with a larger invested fund that one could get to in a week or so, such as the contributions in a Roth.
#2 is rather unlikely, but in a severe economic downturn, such as might follow a widespread natural disaster (Think Katrina in most recent memory), is still somewhat of a greater risk than a true e-fund.
However, a secured line of credit (i.e. a low interest rate credit card that your bank/investment firm provide on condition that your investments are pledged as collateral) is only at risk for #2, since proof of an ongoing income stream is irrelevant; but since you have the same risk since you bank/invest there anyway, it's not greater just because you have a standing line-of-credit as well.