mariaDB not caching queries cached by mysql
There are many different "caches"; not all of them have 'cache' in their name.  The most important is innodb_buffer_pool_size.  An that one is important only if you are using InnoDB (which you should be) instead of MyISAM.  Furthermore, was the Engine of individual tables changed during the upgrade?

Check the table Engines and buffer_pool_size, then report back.  BTW, the buffer_pool should be about 70% of available ram.  And show us the non-cached queries, together with SHOW CREATE TABLE for them.

I see that the Query cache is set the same way.  However, that is usually bad for an active production server.  But that is another topic.

"Drop in replacement" -- mostly it is.  But, as you found out, it is "faster" in some ways, "slower" in others.  Even if you moved from MySQL 5.1 to MySQL 5.5, you might see similar better/worse scenarios.