With Halo going more open world, Gears doesn't need it even more lol Not every game needs to be open world, Gears 5 did it pretty well, only one spot was kinda the hub and you could travel back (reminds me a bit of Tomb Raider reboot) but I wouldn't push for it to be anymore open than that.
Also for halo
Halo 3 > whatever else
I love Reach but damn armor abilities and bloom ruined the MP eventho I played that probably the most out of franchise