The only difference is a bond fund allows you see the true value of your holdings at any given time, where the ladder approach blissfully ignores the increasing/declining value due to interest rate movement and simply holds everything to maturity.
There are some bond funds called fixed-maturity funds that actually mature on a date and pay back the principal. Ie. they let all the bonds inside mature without reinvesting them. iShares iBonds are an example. But this is not the norm for bond funds.
You generally seem to be conflating face (static) value with market (dynamic) value. You're not wrong but your article makes a number of statements implying a ladder is better/safer simply because you refuse to recognize that the current value will deviate from par.
I added: Some readers have pointed out that over the long term there isn't a difference between building a ladder and using a similar bond fund. This strategy assumes that eventually you'll want to move your principle out of bonds and into something else like a down payment (while rates are still rising), but you don't have a well-defined timeline. If you are planning on keeping your principle invested in bonds into perpetuity then a bond fund might be a more suitable investment.
Thoughts?