I´ll write about my experiences with dragon polymorph and combat in Wrath of the Righteous.

There´s a lot of ways to become a weird dragon. The easiest one is>! Gold Dragon Mythic Path!<. Build a Melee character (Full BAB Dragonheir Scion is nice for elemental arcane strike) and reach lvl 8 mythic path. But that means you spend most of the game as a flashy warrior.

Now for classes, i tried these:

• Shaman Build that becomes a Dragon by lvl 9 or 10 (combine spellbook with Angel). You pick spells that boost your melee strikes and select spirits that give you elemental damage per natural attack (Thats Wind + Fire + Earth). You become a dragon with lvl 9 Shapechange spell (thats why i prefer to mix spellbooks, you get those earlier). Elemental Barrage mythic power will melt stuff for you (and you can dip Loremaster for Geniekind by lvl 18).
• Oracle (Focuses on Geniekind) and if you want to use mods, Nature Fang Druid (Mix of slayer study, rogue sneak and druid spells). You become really powerful when you combine spellbook with Angel. Both of those also use Shapechange.
• Sorceror->dragondisciple->eldritch knight, it works well on normal with no combined spellbooks and its very very powerful if you combine with Lich.
• Incredible Might superpower.

p.s.: One big thing is to polymorph into Dragon first, then buff your char into oblivion. That means all your natural attacks get buffed too and will allow you to stack bites (Witch bite and Skald ones). Thats very very nice on shaman, because most natural attacks will also do elemental damage (proccing Elemental Barrage) when you hit lvl 11.

I hope this info helps you, i´m sure there´s a lot of more experienced people that waddled the Dragonways in Pathfinder.