You have a seven person group. Did anyone in your group take the feats? Is your party buffing to assist them? I think you said you had some druids? So faerie fire instead of bless? Faerie fire is really powerful. I want to see what faerie fire and bless do together. You might even be able to stick faerie fire on a legendary creature if they think it is a weak effect that won't damage them. They may just let it happen.
Our group and the advancements they took:
1) Human Variant Battle Master Fighter 6: Heavy Weapon Master, Sentinel, and Great Weapon Master feats.
2) Forest Gnome Ranger 2 Evoker Wizard 4: +2 Int (he had a headband of intellect, but liked his other 3 attunement items more, so he boosted Int and gave the headband to the Rogue)
3) Half Elf Arcane Trickster Rogue 6: +2 Dex
4) Mountain Dwarf Tempest Cleric 6: Alert
5) Lightfoot Halfling Lore Bard 6: Mobility
6) Wood Elf Moon Druid 6: War Caster
7) Half Elf Vengence Paladin 6: Defensive Duelist
So, mostly the PCs have taken feats and GWM was taken once. But, we do not have an archer, and only two PCs use two weapon.
In reality, the party tends to not buff the Fighter because he is so good. Not that they never buff him, but as an example, both the Paladin and the Cleric can cast the Aid spell. The group often casts a 5 point Aid on 3 PCs and a 10 point Aid on 3 PCs. The Fighter usually gets a 5 point Aid because he is just that good. However to be fair, the Bard often gives the Fighter Bardic Inspiration and the party often takes short rests between encounters (so far, they haven't run into many running battles or "time is running out" scenarios where short rests cannot be taken). So the Fighter often has a full complement of superiority dice. This makes a difference because the Fighter can use his dice to get advantage (to cancel out -5/+10) and a bonus superiority die to damage. So he often does that once on his turn. I often throw out encounters to challenge a 7 PC group, so they use up their renewable resources with little regard to saving them because the encounters are challenging and it is often easy to rest.
In addition, the Fighter has Sentinel. His declared purpose is to be a tank (relatively high AC, HWM, second wind, and feint), not a damage dealer (although he deals a lot of damage). He purposely moves his PC into groups of NPCs as often as possible, even taking OAs in order to position himself with the most number of foes surrounding him.
But, a 7 party group runs a bit differently than a 4 party group. The group has 5 PCs out of 7 that can heal. The group has PCs with ACs of 22 (25 with Defensive Duelist), 18/20 (20/22 with Shield of Faith), 18/20 (damage mitigation), 18/20 (23/25 with Shield), 17/19 (often 16 Barkskin wild shaped), 17 (22 with Shield, but can Disengage), and 17 (22 with Shield, but has Mobility). The group often has someone nearby that can heal and most of the group can form a front line (the Druid often wild shapes to large or huge sized creatures, so tends to form a front line by himself).
There is so much overlap and so many options in a 7 party group that the difference from GWM (which the Fighter did not acquire until level 6, so only 2 gaming sessions so far) has not yet become obvious (and our players do not hang out at the gaming forums). As time goes on, I suspect that there will be a party shift. I think that it is inevitable. Players tend to use the best tactics that are easiest to spot IME.
The Cleric does not often cast Bless (usually once per day max), but now that the Fighter has GWM and the Druid (wild shaped multiple attacks per round), I suspect that she might start casting it a bit more often.
The Cleric is primarily a two handed weapon PC, so I could see her taking the GWM feat. And the Halfling does limited damage, so she might take SS and use her Bardic Inspiration to self buff (although she is the primary arcane spell caster at the moment with both Fireball and Haste, so she might focus on being a spell caster).