Yeah, few of the characters are good enough to support a full movie on their own, but if you toss in a ton of them and let them bounce off one another then that becomes less of a problem.
> How are there any real stakes then?
There aren't. these movies play by comic book rules through and through (or TV rules). Nothing is permanent, everything will go on forever (or until the actors quit). this is the season finale that ends on a cliffhanger which will be resolved in the premier of the next season (which will be avengers 4).
If you want to read stakes into it then you could say the emotional impact is that the other characters don't know that these aren't permanent deaths. And for me the bigger curiosity is to see what ridiculous magic/sci-fi method they use to fix everything in the next one.
> And though I'm not a huge Whedon fan, I like his approach
This isn't Whedon. Whedon got snatched up by DC and made the Justice League movie (which nobody gave any shits about). Infinity War is directed by the Russo brothers, who directed all the Captain America movies (as well as directing Arrested Development and Community among other TV stuff before they transitioned to making movies). Their TV experience gives them pretty much the same skills as Whedon at handling big casts with lots of comedy, but they don't have the same baggage he brings.