Well, that wasn't a very diplomatic reply, but hey, there are [censored] everywhere.
No checkpoint in WC: no, it was the 90s, the concept of having a dual progression saving system (in mission + overall campaign) didn't exist. People are used to this now, but I personally can live without it.
Just start over, it's how it was happening in old WC: wrong, the game flow was significantly different:
-->old WC: dialogue with shipmates (skippable), briefing (skippable), in flight (unskippable, chatter is kept to a minimum, little to no down time)
-->WCS: briefing (skippable), in flight + dialogue with squadmates (unskippable, "long" dialogues may occur at any point in the mission, good combat chatter, up to 5 minutes of downtime)
I honestly would have started over the "escort armaggeddon" until I beat it while staying on insane, but after the 20th or 30th time I had to listen to MD's intro, I reduced the difficulty to medium or easy, still lost a ship, and that was it, I turned everyone invincible an sit through the whole thing (I was actually really close to beating the mission twice, but one of the friendly capships TKed another with its CSM, that was hilarious, though rage inducing^^).
tldr; IMO, unskippable cutscenes in video games are a plague that should have been eraticated ages ago. WC's cutscenes were skippable, WCS's equivalent being in the middle of the mission (the prerendered cutscenes and briefings don't count), they are (currently) unskippable.
Is there any point that either of you would like to discuss in more details? I'm not sure I covered everything, and some of what I said is subject to one's own point of view.
Have a nice day.