That piece may be a good article, but it is not written in stone and each game does not have to slavishly obey it.
1. If Larian implements a grid overlay, I hope it's toggleable from a menu. I'd rather have it off.
2. Larian is designing this game for 2 main, 2 henchmen and 2 summons. Changing it to 6 characters would mean a lot of additional redesign and rebalancing work. They don't have to redesign everything for 6 people just because an article says 6 is the golden number.
3. Definitely not all characters can be good at everything, but one of the much-touted features is the magic combo system, so I'll probably be making my characters hybrids. My first one will probably be a STR-CON tank and my other a DEX-SPD rogue, with a smattering of INT and other stats to use magic.
11. Sure, some fights with special objectives and conditions are great - there was the demo of the skeleton bomber with a hostage, Ezio the Orc which you can use a voodoo doll on, and the skeletal mech that was more powerful than the rest of the encounter. But not every single combat has to have extra objectives.