That is certainly not my understanding.
The May withdrawal agreement only kept the UK within certain strictly defined aspects of the customs union and single market for a limited period (the “NI backstop”).
The time limitation on the period was subject to the UK developing technology that operates customs, excise, phytosanitary and other controls on the Ireland-NI border. Since the current UK government says it has already identified how these controls would work, then there was never any reason to suppose that the backstop would have come into effect under May’s agreement. The UK would have been out of the single market and customs union within a year or two.
In any case, the Johnson withdrawal agreement has simply relocated these controls to the Irish Sea. So if you truly believe that the May withdrawal agreement would have kept the UK in the EU, then what we now have, under the Johnson withdrawal agreement, is NI being kept in the EU, and a border being drawn in the Irish Sea. England, Scotland and Wales will be "free", and NI has been thrown under the bus.
You also have to ask yourself why the Johnson withdrawal agreement is what the EU wanted and proposed in the first place. Johnson has simply capitulated to a deal that splits the UK, a deal imposed on us by the EU.