The comparison with the US is not appropriate, as we're talking about very different cadastral situations. The US has, at the time, a wide open western frontier, with enormous quantities of fertile arable land freely available. Britain is a country in which all the reasonably fertile land has long been brought under cultivation. Enclosures apply to marginal land (marshes, poor pasture), in which a few semi-squatting, destitute "cottagers" eke out a very desolate existence. This land can be made fertile, but only with a huge investment of capital (e.g. draining). The way the enclosure act works is that the cottagers are paid some meager compensation in exchange for their grazing rights. The landowner then gains exclusive access to his own land, which now becomes profitable for him to invest in, and transform into very productive arable land. Will the landowner work all this land by himself and eat all the produce? Obviously not. Some of the cottagers are hired locally, as farmers on the newly productive land that requires a workforce. Others move to the city, where the price and availability of food become much better as a result of the improvement. Whichever choice they take, they are no longer half-starved, and at least they have a chance to work for a better future. The alternative you seem to be proposing - dispossess the landowner, distribute the marshes among the cottagers - is not practicable, on account of the large amounts of capital needed for improvement, which only the landowner can reasonably obtain.

This being said, I think we agree on two points: the Enclosure Acts increased the pace of urbanization (but I believe it was by providing cheap food, not forced relocation), and they also increased the prosperity of society in aggregate. On my side, I argue that this prosperity registered a net gain for both landowners and the poor classes.