Thanks for your questions. If you check you will find an article from several years ago: Full-time Work and Eremitical Life (not the exact title). Look at the last portion of that article you will find a bit of information on the meaning of the term semi-eremitical, and more importantly what it does not mean -- at least not any longer. Because I don't agree with you that semi-eremitical life is not truly eremitical, neither can I accept that one form of eremitical life is better than another. Absolutely, one will be better for one hermit than for another but solitary hermits, semi-eremitical hermits, and hermits living in canonical communities are all living eremitical life accentuating in one way and another the silence of solitude; thus, I don't agree that one is better than another. They do accentuate different qualities, demonstrate in different ways the relationship of eremitical life to the larger faith community, and so forth, but they remain forms of eremitical life and each is authentic in its own way. (Clearly, I am not referring in any of this to fraudulent or inauthentic ways of living -- or failing to live -- eremitical life.)
Semi-eremitical life refers to eremitical life lived within the framework or context of a community. It does not mean it is merely half-eremitical (though one might structure the community in this way, somewhat akin to choir monks and donate brothers in the Carthusian tradition) but rather that hermits living in this way are supported in their solitude with some elements of communal prayer, meals, and perhaps, recreation (long walks, a shared movie, poetry reading, a board game on some evening, a trip to get groceries, etc.). The solitude lived is eremitical and it is not half-time. Again, with semi-eremitical life, the context for living one's solitary life is a community, or, in the case of lauras, it is lived within a colony of similarly committed solitary hermits. Solitary eremitical life is lived without the communal context --- though it may involve a laura. Solitary hermits who are consecrated in the Church under c 603 live eremitical life within a parish context and also within a diocesan one. These are ecclesial vocations so there is always a significant ecclesial dimension. This does not make them any less the "real deal" than any other form of eremitical life. Instead it helps assure that the authentic solitude of eremitical life is not supplanted by individualism and isolation.
You ask if life in a laura doesn't constitute a mitigation of full-time eremitical life. I am assuming you mean why doesn't it represent a mitigation of full-time solitary eremitical life, yes? Assuming as well, that each hermit lives her own Rule under the direction of her own delegate and spiritual director, that she maintains care for her own finances, insurance, ministry, education, ongoing formation, retreats, and self-care, a laura will be supportive, yes, but the hermit remains a solitary hermit. The use of the word mitigation here is a bit problematical for me because it seems to indicate a weakened discipline, lessened time alone, etc. The point of eremitical life is not that it be difficult (though it will have difficulties as any other vocation will) but rather that it be healthy and defined in terms of one's communion with God in the silence of solitude. If a laura helps ensure all of the elements mentioned above in this paragraph, then it may actually assist the hermit to go deeper into her own living out of her Rule and vows within a more immediately supportive context.
Maybe an analogy will help here. Some might think that a vow of obedience mitigates the freedom associated with eremitical life. But actually, the vow ensures that the hermit will move more deeply into her life of attentive listening and the freedom of a deepening love relationship with God and God's creation. While it is true the vow will constrain freedom if this is defined in terms of one's power to do whatever one wants whenever one wants to do it, it actually provides limits within which one achieves a greater Freedom to be the one God has called one to be. This latter definition is a Christian conception of authentic Freedom. In a similar way, a properly constituted laura where hermits live their own Rules and maintain a context of the silence of solitude for and with one another, far from mitigating the hermits' solitude, will find they are supported in a deeper and more consistent life of the silence of solitude shot through with the love of God.
But yes, if a laura is a colony in name only and fails to ensure, support, and nourish the constitutive elements of c 603 (one's own rule, delegate, spiritual director, finances, ministry, life with/in the parish, focus on the vows, needs for ongoing formation, and so forth), then this could absolutely represent a mitigation, and in fact a distortion of c 603 (solitary consecrated) eremitical life. I may not have adequately answered your questions so please get back to me as you wish!