Some notes on my end since I compared this iteration of the Artificer class with it's original form in 3.5.
Artificer in general:
The Wondrous item could be expanded a bit more and allow the artificer to repair or recreate said items at a fraction of the cost.
Magic item creation could be expanded more into grafts and infusions. Spell scrolls and spellbooks can be broken down into their magical essence to be grafted onto weapons and armor. I would like to propose that grafted items are non-tradeable in Adventurer's League and can only be shared within the campaign and will only work when the artificer who created them is with the party. Tinkerers could also have their own schematics book where they store their plans for constructs as well as spells copied from spell scrolls. They follow the usual wizard rules on copying spells, but not get any discounts since they don't specialize in them. I do argue that when creating spell scrolls, they should at least get a reduced fee since they will use them either in grafting or infusions, or as emergency spells slots.
Gun variations would be nice and giving the players options on how to customize and improve their weapon like increasing range, clip improvements so that reloading can be done during short rests or when the party is out of combat, since, compared to other ranged users, they can't retrieve their ammo again, stealth options, etc.
Ammo crafting would be nice as well. Giving the option to create elemental ammo as well as ammo for specific scenarios would keep gunsmiths busy during short rests. Downtime activities can be provided for gunsmiths to search for components for their ammo, which would entail a schematics list.
I'm okay with the Mechanical Servant staying for Alchemists and Gunsmiths, but give them options to upgrade them or add features based on the subclass. Gunsmiths can add armaments which will require gold, materials and downtime, alchemists can augment theirs with a delivery system or a portable lab where they can concoct potions and chemicals while on the go.
More variations on concoctions and allow Alchemists to craft their own personal concoctions based on components used, my suggestion would be that the spell components used in certain spells would be the guide on what formulas they can make.
The mechanical servant can be replaced with a homunculus. Give characters on how they will create theirs. Will they grow them from a bottle, tailored to their specifications or go the Frankenstein route, mish-mash body parts harvested from fallen enemies and build your own monster.
More transmutation options. Spells that allow the manipulation of matter should at least be in the Alchemist spell list.
The automaton/construct class. Taking a cue from the Revised Ranger beast enclave, they start out making simple automatons for mundane tasks, like shining a light, providing surveillance by having a connection to the tinkerer through their eyewear, becoming simple traps or alarms. Then by level 3, they build their Major Construct. Sizes vary from Large to lower and the CR2 option can remain. I would like to argue that constructs should at least have higher AC than their biological counterparts and they level-up alongside the tinkerer through improvements or upgrades.
Also, variations on constructs would be appreciated. You could have combat constructs and you can have non-combat constructs. Trap creation would be welcome as well.
I'd like to also offer up a suggestion that higher level tinkerers can make their own humanoid constructs, sort of like a puppet maker. At level 5, they can make a non-combative humanoid construct that can assist them in making more constructs, thereby reducing the duration of making constructs by at least half. And in place of the clone spell, a high-level tinkerer could basically make an automaton version of themselves to replace them in the event of death. Or something similar to Simulacrum as well.