Except he mathematically will have utility spells left over. And a buff-cleric (like the warpriest) doesn't use his spelsl for direct attackign so "spells combat utility will be far diminished" simply isn't true.
There's just no way you can know this. Certainly at level 1 he needs to spend 100% of his spell slots on buffs to match the fighter, and then not for a significant portion of the day. And if he uses crusader's strike and divine favor, he's
not using healing word.
On the topic of something that compensates for many more hitpoints as he levels...
First of all, healing after the fact is a much worse proposition than just having enough hit points to start. Secondly, CLW uses the casting stat; which this hypothetical cleric has dumped. Thirdly, it costs an action, so it's not attractive during combat. Witness 3e's healing which was generally between combats, not during. To be useful in combat, healing has to either be dramatically powerful, or not cost an action - like Healing Word, which, incidentally, doesn't use the casting stat as is and the war-cleric actually knows, unlike CLW. To compensate for the fighters hit points, he'd need to spend a significant portion of his spell slots purely on healing words; and even then this isn't a simple trade since it's after the fact (worse) and cannot be combined with other spells (bad) but can be used on others (good).
So this hypothetical cleric would need to prepare Healing Word to catch up hit-point wise, but that means cutting into precisely those combat buffs that allow him to catch up to the fighter. So you're left with a warrior that has essentially no advantages and can only hope to come even close (but not actually reach fighter levels) for 1/day. That's... not exactly overpowering.
No matter how you twist this, there's just
no way you can take these characters and conclude the cleric outshines the fighter at fighting. Even with
both buffs it's fairly close, and if he does that, he has
no healing, worse hitpoints and the rather significant problem that he can only maintain that level for
1 minute a day with prior notice!
This issue of prior notice is fairly critical to be honest, since while it's fairly common to know enemies are nearby and thus not to be surprised, it's also fairly common not to know exactly when combat starts until initiative is rolled, by which point Divine Favor has the major downside of costing an action. Frankly, with a duration of just 1 hour, I'll bet that during the playtest many people had encounters with the cleric in which even that buff wasn't on. Because if you didn't anticipate that
this combat was going to be the strong one... again, it's going to cost you an action to correct the mistake.
So, I can only wonder whether you're worried about something that just isn't in this playtest - such as worries of 3.5 with persistant spelled self buffed clerics or whatever. Based this playtest, arguing for the warcleric to be nerfed is arguing for unbalancing the game.
Frankly, I don't think I really care to much if that happens by accident or as a side-effect of simplification or whatever. But it's an odd goal to aim at.
You might argue that the slayer theme's first level ability is weak (it certain is in DPR terms), or that the cleric's Guardian Theme is better (it probably is). But that's not an issue with the
class.
Most importantly: Aiming for perfect balance means making tradeoffs in terms of complexity and development time. It's attention misspent. If the imbalance is trivially fixed or particularly egregious it might be worth it - but I just can't see that here; if anything, the fighter looks too strong by comparison; certainly nothing clear enough to be problematic. I'm all for reasonable balance - but this looks more like advocating for your favorite class.