The movie spends a lot of time on the testing and recruitment, making it seem pretty selective because only people in their 40s who would be dead by 2050 are eligible to go. On the other hand, we eventually learn that there are less than 500,000 people still alive in 2050, which should mean that that over 7.9995 of the 8 billion people in 2022 are eligible to go. The chance of testing someone in 2022 that's still alive in 2050 is less than 6/1000ths of 1%, or, put another way, for every 1 million people drafted, only 60 would be disqualified (but, really, probably half that because half of the 500,000 in 2050 wouldn't be alive yet or old enough to be drafted in 2022). Maybe someone should've told them that before they limited themselves to out-of-shape 40-year-olds.
Also, what sense does it make to send ordinary people, especially people with science backgrounds, into the future to act as grunts and die? Wouldn't it be a lot smarter to simply warn mankind and allow those smart people to stay in the present and contribute to 30 years of developing technologies and preparing to prevent or win the eventual war? 30 years of doing what they're good at to try to avoid a losing war... vs 7 days of doing what they're not good at and likely dying to win a war that's already lost. The choice seems clear, but everyone in the film does the opposite of what makes the most sense.
On top of that, why wouldn't they give these people some basic training prior to sending them into the future? They're teachers and scientists. I get that they're in a rush, but can't they spare at least one day to teach them the basics and give them a little target practice? That one guy was just about to jump and didn't know which way to load the magazine or how to turn the rifle's safety off.
Along the same lines, that experienced guy with the trophy necklace knew that the only vulnerable parts on the aliens' bodies were the neck and belly. Why didn't he share that with the other recruits before they got into action or, better yet, why didn't the trainers teach that? I mean, it's no wonder that 80% of people that they send into the future fail to return. They're handing weapons to out-of-shape common folk and sending them into the future without any basic weapon training or tips on what to aim at.
BTW, 30 years into the future, they're still using Humvees, F-22 Raptors and modern weaponry. No wonder they're losing the war. All of their technology is almost 50 years old. You'd think that they'd realize that and, again, tell 2022 Earth to spend the next 30 years developing new advanced technologies that might prevent or win the eventual war, instead.
I liked how Dan returned to the present day with the toxin and we were supposed to think, like him, that he failed. Is having a cure too early ever a bad thing? If you took a COVID vaccine back in time to 1991 and weren't able to bring mass produced amounts of it back to the present, did you fail to stop COVID? Of course not. It's better to have it too early because you're sure to have plenty of it ready to nip the threat in the bud when it finally appears.
Speaking of the toxin, did they actually even need it in the end? They could've simply blown up the dormant aliens with C4 or, to be safe, exploded a nuclear bomb on the ship. In fact, Dan didn't even need to go to the future. If he or someone else had just thought to analyze the claw that the guy had around his neck when they were first recruited, they could've cut out literally half of the movie and gone straight to Russia (after a stop at the local high school to consult the world's premier volcano expert, of course).