It's arguably ambiguous. As you've said, the effect of concurrent infusions applies the effects of three infusions onto a target object with a single action, exactly as if you had cast it. The thing is, if we're going to read that as implying the costs and components of the infusions apply, then you run into different rules holes.
If you're bringing in the experience cost of spell storing item, then you're making a statement that "exactly as if you had cast it" means "you go through the process of casting it." We can't selectively apply just the xp cost if we want to be consistent; at this point, we'd also need to bring in other pieces too. What happens when a spell requires you to make the verbal and somatic components of multiple infusions simultaneously? Can you do that? What about casting times? When would the infusions go off if two of the infusions had a standard action casting time, and a third had a 10 minute casting time? Concurrent infusions has a 1 minute cast time. Does that override them? If so, wouldn't concurrent infusions's "Components: S, M" line also override the experience component of spell storing item?
The only reasonable way of adjudicating concurrent infusions is if it skips past the entire casting, and just applies the effect. Anything else requires a rabbit hole of houserules.
But should it work that way?
In my opinion? Yes, it should. Concurrent infusions is a 4th-level infusion, of which artificers get very few per day. We might have a gut reaction to skipping an XP component on a cast, but let's actually take a look at what the amount being skipped is:
XP Cost: Your caster level × the spell level. For example, to place a scorching ray spell in an item, you must spend XP equal to your caster level × 2.
This is tiny. A 4th-level spell costs sixteen (16) experience points to imbue with spell storing item when you get concurrent infusions at 8th level. Sixteen! You have a total of twenty eight thousand experience points by that point, and the amounts needed per level increases quadratically from there. A CR 8 encounter in a 4-person party awards you 600 xp per character, and you're expected to get that multiple times per day. At 20th level, CL 20, the maximum, your casting of spell storing item for a 4th-level spell is 80 xp. At 20th level you have 190,000 xp. You're spending 0.04% of your experience points on that casting (not 4%, 0.04%).
So, as a frame challenge, I ask you: is skipping that cost really 'insanely broken'? Heck, is it even a big deal at all? The only things that happen in practice if you allow it to work as-arguably-written that happens are:
- The artificer player used a higher-level infusion slot so they don't need to worry about tracking such a trivially-small difference in experience points.
- You can buy a minor schema of concurrent infusions, to give you a 1/day casting of spell storing item at a significant upcharge (since minor schemas can't be made of infusions with xp components, normally).
If you have an artificer in your campaign, neither of these things are going to be unbalancing compared to the more significant strengths of the class (WBL-mancy and crafting).