Ever since Modern Warfare (The original) I don't think anyone has ever said that the single player in either of those games was particularly gripping or even good. GTA, on the other hand has always had excellent single player. That being said, I hope V isn't the Modern Warfare of GTA games. Would be a shame.
I believe if you call in backup as code 3 instead of pursuit they will come directly to you and decide what to do from there instead of joining any pursuits. But yeah, I've had this happen on a few street race events where there are two suspects so I call in a helicopter and chase the one the helo doesn't, catch him and then join the pursuit on the other suspect. Too much fun!
I'm kind of disappointed in the general direction most games are going. They are either bad early access knock offs of successful titles with very little hope of ever being finished, or MMOs based on existing franchises. There are some exceptions but this is the general direction the industry is headed. I enjoy multiplayer just as much as single player but being forced in to a box that R* defines ala GTA Online and the very specific content they created for it is inherently limiting. I got bored of GTA Online after about a week having done all of the heists and most of the other side missions that can be done. I wish I could play modded in a private lobby. And this is only compounded by the fact that there's probably no single player DLC to come.