As with many things in D&D, this answer comes in two flavors.
In terms of rules-as-written, some of the non-instantaneous, non-concentration spells do indeed point out that they can be dismissed. I believe the NDA is still in place, but in your packet you can see that these spells include Disguise Self, Light, Mage Armor, Minor Illusion, and Thaumaturgy. There are other non-instantaneous and non-concentration spells that have no explicit dismissal mentioned, such as Pass without Trace, Speak with Animals, or, as you mentioned, Spike Growth. I was also unable to find any reference in the magic rules to dismissing spells, outside of individual spell descriptions, so I would say that, by RAW, unless otherwise stated, non-concentration spells cannot be dismissed early.
This is where it gets trickier, and I've either found or imagined bits of evidence in favor of both sides. It seems that most of the spells with explicit mentions of dismissal are first-level or cantrips, implying that, if the writers of the playtest started from the lower levels, they might have forgotten that they needed to explicitly state that the spells could be dismissed. However, there are also spells such as Passwall, where it's actually explicitly stated that the spell lasts for the duration. This seems to be an intentional choice to limit the spell's utility. If you can't end it early, you can't use it to open a passage in front of you and close it behind you to escape an enemy. That the writers felt obligated to point out that the spell lasts for the duration seems, to me, to imply that other non-concentration spells without this clause can be dismissed at will. There doesn't seem to be a clear rules-as-intended ruling on this issue, at least not from the packet exclusively.
What should the ruling be?
Ultimately, it's up to your group, or the DM of your group, depending on your social dynamics. Due to the unclear intent, I might personally adjudicate that there is some kind of cost to dismiss the spell. Perhaps it takes an action, as Disguise Self does, to be dismissed. Perhaps to end the spell early, you need to cast it again, in sort of a counterspelling situation. Maybe you need to roll a magic ability check to determine if the spell can be dispelled that round.
Hopefully, we can see this issue be cleared up when fifth edition is officially released. I'm sorry that I couldn't provide a definite answer, but I hope that this gives you something to work with in terms of creating a solution for your group.
It's not OP compared to other 1st level spells.
Consider Burning Hands, which deals 3d6 in an area, or Inflict Wounds, which deals 3d10 damage, or Dissonant Whispers, which deals 3d6 while wasting the target's reaction in order to provoke attacks of opportunity, or Chromatic Orb, which deals 3d8 damage.
While Guiding Bolt is a bit stronger than these others, its secondary benefit is also smaller.
This might be an encounter design issue
If your cleric is only ever casting healing spells and guiding bolt, that means the incentives in each fight are only based on direct damage to one enemy without terrain. One could imagine that save-based spells are better in areas with lots of cover, or AOE spells are better against a larger number of enemies.
Additionally, remember that a cleric only gets a certain number of 1st level spells per day. A ranger with 16 DEX and a heavy crossbow can deal 1d10+3 damage per hit, which averages 8.5 damage, and he can shoot essentially unlimited times per day. With multiattack, the ranger can deal double this damage. On the other hand, a cleric only ever gets 4 first-level spell slots. If you're fighting multiple encounters per day, as you should, those 4 spells will run out quickly, especially if the cleric has to do anything else. However, if you're only having one or two encounters a day, this built-in balance is broken.
The spell listings on D&D Beyond are sortable and filterable for exactly the information you're asking about: buffs without concentration.
At the time of this answer, it only includes the basic rules content, but that will change.