You can do this without the Item.
On the MQTT Broker Thing you can add event Channels. These are subscriptions, often using a wild card subscription, and that Channel can directly trigger a rule when a message is received.
So you would configure the Channel to subscribe to this esp32panel’s MQTT topic and you can configure a separator character (# by default). Then you can choose this Channel to trigger the rule. Inside the rule there will be an event (how it appears depends on the language) which will consist of <mqtt topic>#<payload>.
The MQTT EvenBus rule template works off of this feature. It subscribes to all messages below a given point and triggers a rule on any received message. The rule parses out the topic and message and uses that information to keep an Item in sync with an Item of the same name on another running OH instance.
But the OH architecture is built with these layers of Items and Things on purpose and for a reason and I can’t imagine that changing for one binding among hundreds. Much of what makes OH unique and powerful is enabled by its architecture.