is it typical to match opponents of ridiculously uneven size?
Not always right away, no. Depends on the level of confidence of both parties. Especially for combatives -- the kicking and punching. Below a certain size, you just don't want to be holding repetitively for strikes from a big person.
However, for the self defense, the escapes from chokes etc, it's very important to try them against a lot of different people, of very different sizes and shapes, because no two people attack the same way. Groundfighting and sparring are also very different with different sizes.
At about level 2 (4 or more months in) I have told women to mix it up and work with bigger people. By green belt, it's official -- if it's safe, they'll have you sparring with anyone in the room.
Unrelatedly:
Lois & Clark: The New Adventures Of Superman star Lane Smith has lost his battle with neuromuscular disease ALS and died in California, according to internet reports. The actor, 69, played Perry White in the hit TV series. In a posting on Superman fansite Kryptonsite.Com, a family statement reads, "Thanks for your concern and good wishes and prayers. We are sorry to tell you that my uncle Lane Smith died yesterday, a blessed relief from his ALS. Thank you so much for your support." Smith's other credits include roles in Red Dawn, Air America and The Mighty Ducks.