Thing is, Pika doesn't really have trouble keeping up with opponents due to the things he can do out of his Quick attack cancel. Tink on the other hand needs his space on the ground. If he doesn't keep the space people like MK and Marth are going to give him trouble because he can't get them off him unless he regains his space. Of course in matches where he does control the space the opponent is going to be hard pressed to get in and even then they will have trouble as Tink can get them off him.Both Tink and Pikachu have good match ups against DDD, but pika fits the last one more. Plus, Tink can spam projectiles and doesnt really need to keep up with people, while pika's jolt is ground based, and cant take the likes of MK.
This also applies to the situational part. The quick attack cancel can be used in pretty much any match-up and his down-smash and up-smash to thunder combos can be used as well. Tink has to have control of the stage or else hes going to have problems. His projectiles can be really effective in one match-up but can be useless against someone like MK who can get past them and really bother him. He also has to watch out for people with more range and faster attacks then him as once they get close Tink has few options.
Basically Tink fits the hint better than Pikachu.