(History lesson...)
MySQL started out lean and mean. CREATE/DROP INDEX mapped to ALTER because that was 'lean'. ALTER always rebuilt the table because that made the code quite lean.
Eventually the "InnoDB plugin" in 5.1 got smarter. See:
http://dev.mysql.com/doc/refman/5.5/en/innodb-create-index-overview.html
And "Fast Index Creation" became standard for InnoDB (no syntax changes needed) in 5.5.
By that time MyISAM was becoming an unsupported orphan. It continues to look like MyISAM will not get much more attention than an occasional bug fix.
(back to your question...)
So, I recommend you switch to InnoDB and at least version 5.5. In 5.6.7 more ALTERs can be done without copying the table. 5.7 makes more improvements.
Some competitors can even let you ROLLBACK a DROP. But you can't use ROLLBACK until you get to InnoDB.
REPAIR TABLE won't be needed on your 10GB table once it is in InnoDB. (However, it will be 20-30GB.)
When switching to InnoDB, check on the few things that could bite you:
mysql.rjweb.org/doc.php/myisam2innodb
But otherwise, InnoDB is the way to go; MyISAM is passé.