This is just not true, I'll give you an example of the DPS phase alone from Golgoroth fight which lasts 20-25 seconds. This is what happens in those 20-25 seconds
- Bubblebro builds bubble to protect the team, blind the adds and provide damage/defense buff
- Stormcaller/Hammerbro clears out the adds
- Nightstalker tethers the boss
- Gunslinger uses Nighthawk to do mass damage
What is this if not class synergy?
A lot of that isn't necessary on normal mode. And most synergy revolves around titans using a bubble and hunter using a bow. The amount of synergy is very limited. Here are some samples that could allow for more synergy.
Titan can temporarily increase his armor significantly while causing enemies to aggro on him.
Hunter can temporarily increase his damage output significantly while losing a significant amount of armor
Warlock can create walls that keep enemies from entering from a particular side (not as protective as a bubble)
Titans can deploy ammo drops
Hunters can restore ability cooldowns
Warlock can sacrifice his super for an immense amount of light production for teammates
Titans can intimidate adds
Hunters can mark enemies to be always visible
Warlocks can temporarily time freeze adds (they cannot be hurt when frozen)
I could go on. I am not saying that the classs should have all of these abilities at once. But giving these kinds of abilities to classes would allow them to be more diverse. My hope is that Destiny 2 will play at a larger scale that allows for more diversity in classes.