i could see a use case for your fighter changing to Ranger in order to gain a few spells... perhaps even a teliport if they swap low or are plain to reach bigger levels
as for
[ will have to rely on Polearms for extended range]

that assumes you have stamina to use it without falling asleep and of course don't wont to use a bow

is this a standard 6-8 man party we are talking about?

I seem to be in the small minority of people that value quality over speed; That is, I prefer (as close to) perfect parties as possible. This seems to be the perfectionist in me.

Therefore, I grind as hard as possible in the Monastery, especially magic skills (a lot of the magic realm skills can't be trained in Arnika, once you start fighting Savant Slashers and Minion). Try casting Sleep, Itching Skin, etc. against them. You're much better off maxing your magic early, in the Monastery, with no friendlies in the way, and your magic actually works.

Of course, the way I go, a standard 6-man/woman/he/she/it/they/them party is par for the course (I don't care about pronouns; Take it to Facebook). No RPC will ever be able to keep up with my party, except for the quick Arnika Myles/Vi Domina quests where you bring Myles to Vi, and bring Vi to Braffit and He'Li. Also, Drazic and Rodan (you should have portals set to their leaders by that point in the game).

I don't like class changes, as I feel that it dilutes their purpose in the game. Once a Fighter, always a Fighter (getting magic late is pointless, especially if you have 4 portal casters, as I have).

A Ranger can use a Polearm for extended range, and Bows in the weapon swap, so they are versatile. A Human will have good Strength, Piety, and Vitality, so good Stamina, so they shouldn't be napping.