As everyone already said on here, Magic is typically the way to go. The Megido line of spells is absolutely amazing in 4, meaning that Flynn can easily sweep his way through most, if not all, normal enemy fights. If you do it, just keep pumping Magic with a few points to Agility here and there (something like 4/1 for Magic and Agility or 3/1/1 for Magic, Agility, and Luck if you want a point to Luck for status avoiding also).

That being said, a physical build isn't completely unviable by any means, however, with an asterisk next to that statement. The problem here is that, to be honest, the Strength stat is completely pointless. Physical skills benefit more from Dexterity than Strength. If you want this build, you'll probably want 3/1/1 for Dex, Agi, and Luck, with the occasional 2/1/2 level-up. The main way for physical to compete with Magic is the crits towards the end of the game, so luck is a very important stat, but prioritize Dex over it at least.