To me there's a decent amount of experience available without pet pal, though I did do a couple of fights underleveled. I killed Migo after giving him the yarrow with a party of level 2s (though had to rez two members), and then did the fire slugs underground. It's tough, but satisfying. I found I just have to be liberal with my item usage. Spending a lot of time crafting stuff and selling what I don't need for a profit would probably make it a whole lot easier too.
I do think the beginning would be very tough on tactician mode, especially without Pet Pal, though extra enemies might also offer some more XP.
