It's not really relevant to a "force windows classic" mode because the listed bugs are mostly interactions with new features.
The claim that they would have had to sacrifice significant other features is a strawman.
And they're doing the work anyway for the next service pack, apparently...
There were a lot of reasons the old start menu was removed. I listed some technical reasons why "just leave it in as an option" isn't as easy as it sounds.
It is not a straw man to say that investing in one area means you have to sacrifice in others. This is what we call software development.
Features are not added in service packs, and I don't even think service packs exist anymore (service packs are just collections of security and reliability updates, created and packaged together by a special "sustained engineering" team, not the product team).
The product team is building a new start menu option for a future version of Windows. It's a significant undertaking, not something they're throwing together willy nilly. They don't have a time machine, so they can't go back to 2012 and ship it then.
Security Center
Popup Blocking in IE
Image Blocking in OE
DEP
Some others I can't remember