It isn't important to have a ranger or rogue. In fact, I'd say you're doing a disservice to your party by having a scoundrel-based character since it's arguably the weakest of the physical damage groups. Huntsman builds are INCREDIBLY powerful, though, so long as they are built correctly. Scoundrel suffers from a variety of issues, the biggest being sub-par damage output but finesse armor also doesn't give you much physical or magical armor, so you will be incredibly squishy and that isn't ideal for a front-liner. All together it results in a pretty sub-par physical class. It's a bit fun, just underwhelming.
Warfare/polymorph is actually a really strong combination, but I wouldn't worry about putting more than a couple of points into it to get some basic abilities like Tentacle Lash (scales with strength so it's a good heavy hitter early game, but doesn't benefit from crits unless you take the talent that allows spells to crit, which isn't really worth it as there are better talents), Wings is a decent extra movement ability, and some others can be great utility but aren't necessary. Throwing some necromancer in can also be pretty helpful, it also pairs well with the Living Armor talent. Warfare will shine the most using a 2-hander, you get some insane damage output with it. The last game I finished, my warfare guy was 10 warfare, I think 3 poly so I could get skin graft, and the rest into necro. The results of most turns would be me going from nearly dead to full health and magic armor with just a few heavy hitting swings. It's glorious.
I always had a hard time mixing my party with hydro/aero and geo/pyro mages because you rely so much on status effects to get the most out of them, but they tend to cancel each other out. Fire will unfreeze a frozen target, geo will replace water with oil/poison, fire will replace water with steam, etc. It can certainly be done, but it is a pain to manage in my opinion. It works a bit better with a summoner since you can use any surface to get any incarnate type, so you might actually have a pretty solid method going.
My recommendation if you want to change anything, is to get a huntsman character. Ideally you'd want to start putting a couple of points into huntsman, then start putting the rest into warfare since that maximizes your physical damage, then start putting more points into huntsman. Huntsman only increases the damage you do from high ground, and while that is insanely powerful, warfare gives you a straight increase to all physical damage so it's more lucrative to boost that first. The great thing about huntsman classes is that they get all sorts of magical arrows throughout the game, so they are a great support for physical or magical classes. And the damage they do becomes insane by the late game if you utilize high ground as much as possible.
Overall, this game allows you to do quite a bit with your party makeup, and just about anything is viable on difficulty below tactician. Even on tactician you can make anything work, so I wouldn't sweat your choices too much.
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