It seems like it should be-
SELECT * FROM users u JOIN last_user_event_1 e USING (user_id,user_group);
--OR--
SELECT * FROM last_user_event_2 e;
for them to produce the same result set, since the last_user_event_2 already (could) have users info in it very simply by select * instead of e.* in that view definition.
Are there other important joins/where/order by/limits that would be on this "main query" that is just SELECT * FROM ____ right now which you have dropped to try to simplify the example?
You're right about the queries, I made a mistake.
Yes, I'm going to filter them by user_id and user_group, possibly (but not likely) using LIMIT 1. In the explain examples I am using user_id = 1272897 and user_group = 19117