Magento 2 – How to Correctly Update Product Programmatically

The Context:

By decision of the client, the Magento Administrator cannot add products by himself, all he can do is edit them, therefore the addition of products must be done programmatically. There are some "attributes" that he cannot edit as well, only programmatically (sku, available qty) and there are attributes that are merely columns in catalog_product_entity and they are not shown in Product Edit Page. Therefore i've created the following method that creates or updates the products (this products are managed by a third party in their own db).

protected function processProducts($products) {

    $dbProducts = json_decode($products, true);
    $catalogConfig = $this->_objectManager->create('Magento\Catalog\Model\Config');
    $attributeSetId = $catalogConfig->getAttributeSetId(4, 'Default');

    foreach ($dbProducts as $dbProduct){

        $product = $this->productFactory->create();
        $productId = $product->getIdBySku($dbProduct["id"]);
        if(!$productId) {
            $inventoryQty = ($dbProduct["inventory"] > 0) ? $dbProduct["inventory"] : 0;
            $isInStock = ($dbProduct["inventory"] > 0) ? 1 : 0;

            $product->setTypeId(\Magento\Catalog\Model\Product\Type::TYPE_SIMPLE);
            $product->setAttributeSetId($attributeSetId);
            $product->setWebsiteIds([$this->_storeManager->getWebsite()->getId()]);
            $product->setStatus(\Magento\Catalog\Model\Product\Attribute\Source\Status::STATUS_DISABLED);
            $product->setQuantityAndStockStatus(['qty' => $inventoryQty, 'is_in_stock' => $isInStock]);
            $product->setStoreId(\Magento\Store\Model\Store::DEFAULT_STORE_ID);
            $product->setVisibility(\Magento\Catalog\Model\Product\Visibility::VISIBILITY_BOTH);
            $product->setName(utf8_encode($dbProduct["name"]));
            $product->setSku($dbProduct["id"]);
            $product->setUrlKey($dbProduct["id"]);
            $product->setLastPrice($dbProduct["lastCost"]);
            $product->setLastPriceDate($dbProduct["lastCostDate"]);
            $product->setProductGroup($dbProduct["group"]);
            $product->setProductSubgroup($dbProduct["subgroup"]);
            $product->setWarehouseQty($dbProduct["inventory"]);
            $product->setTransitQty($dbProduct["transit"]);
            $product->setSoldQty($dbProduct["sold"]);
            $product->setIsdb(true);
            $product->setIsMassupdate(true);
            $product->setExcludeUrlRewrite(true);
            $product->save();
        } else {                
            $inventoryQty = ($dbProduct["inventory"] > 0) ? $dbProduct["inventory"] : 0;
            $isInStock = ($dbProduct["inventory"] > 0) ? 1 : 0;

            $product->load($productId);
            $product->setStatus(\Magento\Catalog\Model\Product\Attribute\Source\Status::STATUS_DISABLED);
            $product->setLastPrice($dbProduct["lastCost"]);
            $product->setLastPriceDate($dbProduct["lastCostDate"]);
            $product->setProductGroup($dbProduct["group"]);
            $product->setProductSubgroup($dbProduct["subgroup"]);
            $product->setWarehouseQty($dbProduct["inventory"]);
            $product->setTransitQty($dbProduct["transit"]);
            $product->setSoldQty($dbProduct["sold"]);
            $product->setIsMassupdate(true);
            $product->setQuantityAndStockStatus(['qty' => $inventoryQty, 'is_in_stock' => $isInStock]);
            $product->setIsMassupdate(true);
            $product->save();
        }
    }

    $indexer = $this->_indexerFactory->create();
    $indexerCollection = $this->_indexerCollectionFactory->create();
    $ids = $indexerCollection->getAllIds();

    foreach ($ids as $id){
        $idx = $indexer->load($id);
        if ($idx->getStatus() != 'valid'){
            $idx->reindexRow($id);
        }
    }
}

The problem:

When the algorithm executes the if-part of the statement the products are created without problems or errors and they can be edited in Admin Panel (i.e. change product name, visibility, meta title, etc). Nonetheless, when they are updated programmatically (when the algorithm executes the else-part of the statement) the new product's columns are updated without problem but after product->save(), updating attributes like name, visibility, meta title in 'Product Edit Page' doesn't work anymore.

The question is: How to correctly update products programmatically?

PD:

I don't know if it's relevant or not, but the creation of the new product's "attributes" (new columns in catalog_product_entity) was done through the following UpgradeSchema.php::upgrade method.

/**
 * {@inheritdoc}
 * @SuppressWarnings(PHPMD.ExcessiveMethodLength)
 */
public function upgrade(SchemaSetupInterface $setup, ModuleContextInterface $context)
{
    $setup->startSetup();

    if (version_compare($context->getVersion(), '1.0.4', '<=')) {

        $table = $setup->getTable('catalog_product_entity');
        $columns = [
            'last_price' =>
                [
                    'type' => \Magento\Framework\DB\Ddl\Table::TYPE_FLOAT,
                    'nullable' => true,
                    'comment' => 'Last Price',
                ],
            'last_price_date' =>
                [
                    'type' => \Magento\Framework\DB\Ddl\Table::TYPE_TEXT,
                    255,
                    'nullable' => true,
                    'comment' => 'Last Price Date',
                ],
            'product_group' =>
                [
                    'type' => \Magento\Framework\DB\Ddl\Table::TYPE_TEXT,
                    255,
                    'nullable' => true,
                    'comment' => 'Group',
                ],
            'product_subgroup' =>
                [
                    'type' => \Magento\Framework\DB\Ddl\Table::TYPE_TEXT,
                    255,
                    'nullable' => true,
                    'comment' => 'Subgroup',
                ],
            'warehouse_qty' =>
                [
                    'type' => \Magento\Framework\DB\Ddl\Table::TYPE_INTEGER,
                    'nullable' => true,
                    'comment' => 'Warehouse Qty',
                ],
            'transit_qty' =>
                [
                    'type' => \Magento\Framework\DB\Ddl\Table::TYPE_INTEGER,
                    'nullable' => true,
                    'comment' => 'Transit Qty',
                ],
            'sold_qty' =>
                [
                    'type' => \Magento\Framework\DB\Ddl\Table::TYPE_INTEGER,
                    'nullable' => true,
                    'comment' => 'Sold Qty',
                ],
            'is_db' =>
                [
                    'type' => \Magento\Framework\DB\Ddl\Table::TYPE_BOOLEAN,
                    'nullable' => true,
                    'comment' => 'Is External Db Product',
                ]
        ];

        $connection = $setup->getConnection();

        foreach ($columns as $name => $definition) {
            $connection->addColumn($table, $name, $definition);
        }
    }

    $setup->endSetup();
}

Thanks,