So, it's no news that Maxwell is not the best character. Besides gathering resources, he poses no danger during the fight for even with the top notch armor, he's ultimately very, very frail. I think he deserves not much a buff, but a fundamental change to the Codex Umbra.
I came with an idea on how to fix Maxwell. A set of ideas, that is. The first thing would be enhaning his gathering puppets AI to make them chop or dig ONLY when Maxwell's holding respective tool. And when the puppets would be doing so, avoiding the trees Maxwell will chop soon - so basically, choosing the farthest available tree whenever Maxwell is in a highly clustered set of trees - like every wood farm.
The second and the most important thing are his warriors. The definition of useless - dies in a single or a few swings and deals nearly no damage. To buff them, I would suggest allowing Maxwell giving his shadows items such as better weapons or armor. These items would be lost indefinitely as the puppets die, but would never be destroyed when onnpuppets. Armor would grant only 1/3rd of its defensive power. It would be very useful if Maxwell could "feed" his puppets additional Nightmare Fuel to grant them bonus HP - 75 for each piece and 25 for each piece beyond 3rd. These fighting minions would slowly regenerste their health outside of combat.
regardless, the minions would always drop a single piece of nightmare fuel.
The last thing Maxwell would need to top the rework off are some kinds of booster shots for his sanity, allowing him to hire theoretically infinite amount of puppets - produced with some nightmare fuel, bee sting and 2 papyrus.
The idea behind this rework sprouts from my experience of 500 days of Maxwell and subsequent 1200 days of WX-78. Maxwell simply doesn't get any better than 2 free chopping guys. I think that having the possibility to sacrifice industrial amounts of nightmare fuel (every 400 HP minion with a night sword and a nightmare armor costs 18 noghtmare fuel, and 26 for each beyond the 2nd. It is a lot) for external, permanent buff such as WX's would fit extremly well with Maxwell's story and his powers.
There may be some balance issues, but there's plenty of aspects to work around - minions HP, damage modifier, armor effectiveness, hp re-gaining, hp scaling off nightmare fuel pieces, even the cost of puppets and insanity syringe.
given enough love, Maxwell would really become one of the most fun and rewarding characters to play. And I would love to try out such a character - high risk, high reward, versatile and very good in the late game. That's what Maxwell should be in my mind.
I hope you like the idea and if you don't, let me know what part of this extremly balanced not at all broken rework do you not enjoy. Cheers!