The "It's only Villa" argument isn't as straightforward as you make it out to be.
Squad rotation is a must for any club that wants to target honours, hence, given a match against Dortmund and one against Villa, Europa League, Champions League, whatever, you would have to pick the stronger side for Dortmund. Unless Villa were in any way a threat to our position, which they are as good as relegated, there is no argument.
Yes, you cannot underestimate any opponent, but the team that went out for Dortmund should have had no problems beating Villa, even if it were just 1-0- and that's when they should have played.
Now, it's a bit of a clusterfuck. "Throwing" any match is stupid because there is no guarantee you will even win the one you were prioritizing. But, of the four matches, Villa were the weakest and clearly the best match to have a second team play. Or will we muddle through all four with a mix because of criticism and stakes and whatnot? Dier could have easily been rested for both PL games as opposed to the EL. He picks up a yellow against Villa and he misses Liverpool, if it's against Bournemouth, then Liverpool and one of United/Stoke/WBA (can't remember) which are all clearly more of a threat. So, there was an effective way to manage, Pochettino failed to do that. I hope we crush Villa, have a chance against Dortmund and win against Bournemouth- but even if it turns out well, it does not mean that a mistake was not made. Similar to Levy not getting a striker, even if we win the League.
After we exit every Cup, we have assholes saying "Good, we can focus on the League" and yet, we did no better last year after we were cunted out of the EL. This logic is retarded. Mentality is clearly not a strength of the team or the supporters- and that has to change contrary to what some of our fans are satisfied with.