nope, sell them, i even sell UR i think are useless, like the Legendary Fisherman, you summon it and what? You cannot boost its attack with umi on the field, and enemies can attack you directly if it is the only monster u have on play, another one would be insect queen, which i think is hard to do a consistent deck, it needs a sacrifice to attack, sure it summons tokens to ressuply it self
but to attack on the turn you summoned it you need 3 monsters, and that is not all, it gets only to 2600 attack, which other lvl 7 monsters already have from the beggining, sure using pinch hopper can easily summon it, but i feel empress mantis does the job, and dont forget insect princess with paricide parasit.
insect queen works well with pinch hopper meaning you only need 2 monsters and that's pretty noob if you think it's useless. The good thing about the legendary fisherman is that if you have a monster with incredible defense e.g. labyrinth (3000 defense) then you can keep attacking your opponents monsters