Keep in mind that that would make them very powerful as delay skills - and they, especially grenader, are already very powerful.
I'm not sure I agree that they're
very powerful. Sure, they're instant-effect skills which also delay the lemming, and allow the lemming to remain in the same spot - that's powerful, no question.
However, they also have many limitations:
Spearers, by themselves, cannot be used to get the lemming that throws the spear off the ground (that is, from a small platform or pit area). They also require large quantities to be provided in order to build a sufficiently large bridge to cross, say, a water pool. Furthermore, whilst they
can be used to make a "blocker", this requires ideal positioning and, sometimes, very fiddly execution - such as when 2 spears need to be placed perfectly side-by-side.
Grenaders, now that they have the smaller crater, again require large quantities to make it through a sizable chunk of terrain. They also, by themselves, cannot be used to remove terrain immediately beneath the thrower's feet (and are therefore
not "replacement bombers", as such).
The range/arc element of the skills can also be limiting: if a platform is too near the top of a level, the projectile is useless since is simply disappears offscreen. They also require a navigable area that's at least the length and height of the full arc in order to be immediately useful; otherwise, other preparatory measures must be taken to ensure their usefulness.
A good example of this is in the attached solution to Crazy 4
Lemming Express for the 4-skills-only challenge. Note that, in order to throw a
single spear to turn the worker lemming around at the end, it's necessary to blow many holes in the terrain above the lemmings to clear a path
for that spear.
So, are they powerful? Sure! Are they
very powerful? I would argue not so much. Are they
too powerful? Definitely not.
Since the proposed state would change the length of time they remain on the spot, for better or worse (i.e. sometimes it would be shorter, sometimes longer, depending on the layout of the map and the location of the thrower), I'd say this would be a good move to a) add further definition and uniqueness to the skill, and b) enhance and refine its usefulness
as a delaying skill.