RE: Lincoln
The problem is that they really want us to care about him but he's done nothing to warrant that yet. It actually mirrors some of the issues they had back in season 1 when they introduced a whole new cast of characters and started positioning them like the audience had already grown attached when in reality we had no reason to. When the initial cast started to gel and the chemistry began to build, that's when it started feeling like a group of characters worth being invested in, and unfortunately for Lincoln, he really doesn't have believable chemistry with anyone currently (he's had almost no opportunity to build any), and primarily saddling him with Daisy feels very forced. (Even in Joey's single appearance, he's already had more believable and engaging interactions with Daisy and Mack.) Lincoln is too cut off from everyone else, and trading on his good looks is not enough to prop him up. They need to let him actually interact with other characters beyond Daisy, because he's doing her arc no favors, and it serves his character very little beyond a trite romantic sub-plot. Even in the Inhuman camp, almost all his scenes were tailing Daisy around. He doesn't have the charisma/presence of Ward, so having him be so isolated from every other major character is not in his best interests.
They need to think back on how they introduced Mack, Bobbi and Hunter. They were immediately successful due to the fact that they let the characters live beyond their pre-set role of "outsiders". (It also helped immensely that all three actors have a very natural rapport with pretty much everyone on the team.) SHIELD is so strong now because it has embraced being an ensemble cast, and that's something they should definitely keep at the core going forward.