To me, a BIG issue is that infusions are just spell of another name.
So a 3.5 artificer is just an armored caster with a its own spell list which includes object targeting object. A direct conversion is a wizard subclass.
How many other classes fall into that description? Warlock? Bard? Ignoring the agency of "PHB1 class", the problem has been that everyone who comes in and says "artificers are just a subclass" CANNOT justify why other classes like druid, bard, or ranger are, except "PHB1 rule" or "WotC chose to make them unique".
Lets compare things a wizardficer (UA) can do vs. a 3.5 artificer.
* A 3.5 artificer can fight with simple weapons and wear armor. A wizardficer cannot do either of these without multiclassing or multiple feat sinks.
* A 3.5 artificer can find and disable traps. A wizardficer only gets access to Perception/Thieves tools by picking certain races (elf), backgrounds, or investing 250 days/gp in learning the skill.
* A 3.5 artificer can make and use any wands, staves, rods, rings, wondrous items, and other magical items. A wizardficer can make scrolls, potions, two temporary magical weapons or armors at a time, and a few simple items at 14th level. He can only use the items that any wizard can use.
* A 3.5 artificer can make a hommoculus. A wizardficer cannot.
* A 3.5 artificer and augment magic items (gaining bonuses to use them, or using metamagic on them). A wizardficer cannot alter or change magic items.
* A 3.5 artificer gains bonuses to making items (reducing time, cost, and/or XP). A wizardficer gains no bonuses to making permanent items. (indeed, except for 14th level; the class doesn't even reference the item creation rules in the DMG).
* A 3.5 artificer's spell list is limited: buffs, a few creation spells, some walls, some construct affecting spells, and a few that change magic items properties. His spells take a minute to cast (unless spending an Action Point) and almost always only affects items. A wizardficer has access to all wizard spells; magic missile, charm person, animate dead, etc. Additionally, he lacks spells in 5e that clearly seem artificery (swift quiver, elemental weapon, ability enhancement).
To put it a different way, I ran an Eberron game a while ago. I had three artificers; one who specialized in constructs and buffing, one who was a warforged self-buffer, and one who liked to make items (the batman artificer). The 3.5 artificer artificer handled all three concepts, the 4e one handled two well, and one ok, and the 5e wizardficer handles none of them well.