About loners:
It's really not that different if I watch how my friend's character makes a furious special attack in a battle my character is fighting too, or if I watch it while my character is off trying to lose the guards that are chasing him after that misunderstanding with the king. Both times I am not doing anything while the other player does his thing, and then it's my turn again. Whether I get to act for 1 minute every three minutes, or for 5 minutes every 15 minutes, my playing time remains the same.
I am not really bored by listening to what other characters do, even if my character is not present, as long as it is interesting. I'd be bored listening to boring scenes even if my character is present.
Where having characters be together shines is when they interact and talk with each other - but there's not much you can say in 6 seconds while you cast a spell or make a feint, so that's not too noticeable in combat.
No, there is a difference.
If you have a "semi-solo" part of the adventure where one character is doing his "lone-wolf"/"hack the matrix" thing, you are watching him making several decisions and seeing him pass or fail. But only the final result after that "solo" part will affect your next decisions. Every single decision and every single pass/fail in a "round-by-round" situation informs your next action. Every decision and every outcome is meaningful.
"Hmm, the Rogue decided to shift one square to get combat advantage. That means I need to move a square to cover him in my protective Aura"
"The Fighter marked this opponent - I think I can risk provoking an opportunity attack with my ranged attack against him, instead of holding back because I am immobilized."
"Okay, now the Decker defeated the encryption. Now he is dowloading the file. Oh, an IC detected him and attacks. Now the Decker rolls his first attack, dealing damage. Now the Ice attacks him, but the Decker evades the attack. Now the Decker attacks again, but fails. Oh, now the IC has a lucky roll, and the Decker takes some damage. The Download is finished! The Decker makes a last blow at the IC. Almost defeated, but its still standing. It doesn't hit on its attack. Now the Decker decides to log out instead of continuing the fight. And succeeds. So, Decker, let's look at these maps you downloaded."
I am not saying the Decker combat would necessarily be uninteresting or without exciting. But you are still just watching, not interacting. It doesn't even matter whether you watched or didn't watch, you couldn't influence the outcome anyway. If you had gone to the loo, ordered a Pizza or played Dawn of War on your PC, it wouldn't matter. There is a string of events that has no direct impact on your decisions. You are less engaged.