I think it's because our teams are polar opposites in style. My team is Ryoma + Nowi + MRobin, so I'm full of tanky characters who can bait and counter. What I want is a glass cannon-style ranged unit so that I can initiate strong attacks and get kills if I find a unit out of position. Robin is good for getting ranged kills on units he's strong against (which admittedly is a lot of units), but he still doesn't have the firepower that Linde has. I feel like Linde would be able to nuke the tougher characters better than MRobin. If she got a Blade tome, she would probably become capable of nuking most characters in the game, though I'd need to insert a buffing character to support her.
Unless I'm wrong about Linde and she's not as good at nuking people as I think she is. I could be falling for a grass-is-greener sort of thing.
Since the rest of your team is squishy, it makes more sense to have MRobin over Linde since Robin is a good (but situational) tank. But I think Linde could give my team a good bit more punch than it has right now.