[
  {
    $group: {
      _id: "$productId",
      name: {
        $push: "$name"
      }
    }
  },
  {
    $lookup: {
      from: "product",
      localField: "_id",
      foreignField: "_id",
      as: "p"
    }
  },
  {
    $unwind: "$p"
  },
  {
    $addFields: {
      sizeP: {
        $size: "$p.variants"
      },
      sizeName: {
        $size: "$name"
      },
      isMatch: {
        $eq: [
          {$size: "$p.variants"},
          {$size: "$name"}
        ]
      }
    }
  },
  {
    $match: {
      isMatch: false
    }
  }
]