I’d be fine with it working that way, personally, but I’ve been told that that isn’t sufficient spellcasting ability to express the Eberron Artificer. The suggestion of spell slots powering Infusions was meant as a compromise. An alternative where both full-spellcasting and non-spellcasting could coexist in the same class. Personally, I don’t much care how it gets done, as long as it is possible to play an Artificer who doesn’t cast spells and is still a fully contributing member of the party.
Err... The Artificer in the playtest does get Extra Attack at 5th. Technically it’s slightly more restrictive than Extra Attack, but since you can Infuse a magic weapon for yourself if you need it and it counts as Extra Attack for multiclassing purposes, I’d call the current Artificer a martial by this definition.
I don’t see any reason spellcasting via subclass needs to be 1/3 progression. Have the subclass kick in at 2nd level and give them half-casting via their subclasses. As long as there’s one that gets something else, like extra Infused Items, or a more powerful pet, or bonus ASIs like the Fighter and Rogue get. Anything, really, as long as there’s an avenue for playing a non-casting Artificer.
Of course, I know it won’t happen. They didn’t give us an option for non-casting rangers, they’re not going to do it for Artificers. But as long as this thing is still in play testing, I’m going to keep giving the feedback that I and others want a non-spellcasting option for the class.