1. it's not just that. the transporter does decompose and compose your body from a saved pattern prior to the energizing process. all it would take to "remade someone into a younger person" would be a stored pattern or in this case a "space-time anomaly". why the Feds do not have stored patterns of themselves and therefor the key to iternal youth is another question. perhaps the pattern could/would override their neural network as well, thus reverting them to their former memories. 2. besides, the being was not compressed it was shrinked. do you recall it retained the exact same shape and proportions which is not likely to happen if gass gets compressed. 3.Q were defacto responcible for the anomaly. seing how Q resented suicide, it makes no sence at all they would risk their own destruction by inducing an anomaly that would destroy them. unless they were eighter imune to it, or could stop it any time they wished so. since they seam able to manipulate and create space-time and alternate realities i'd say its safe to asume they are a tough opsticle to tackle. 4.not just that, E.T. and ST are in different universes, X-Men and ST too. in ST the end of the 20th century was marked by the Voyager probes (not just 2) and the Eugenic Wars. bot events (especially the latter) is unique to the ST universe... and TWS, multiple realities and timelines are a part of the multiverse.