The idea of grenades has been addressed and slaughtered several times; not as often as pets or dual wielding but enough times for users to be expected to realize the unavoidable facts:

Bombs are designed to be area of effect but require the user to stay in proximity of the target(s) with the chance of being hit to balance against the damage rate advantage. Guns are designed to fire from a safe distance with minimal risk of being hit to the user but with less damage and far less area of effect. These two weapons are opposites in all major aspects. If you want a crossover, see Catalyzer; that is the closest we will ever get to a bomb-gun hybrid. Also, I may be incorrect to point this out due to vague wording, but you seem to indicate there is a 1* of the grenade line; do you know why Haze became its own line starting at 2* from originally being the 1* base of all vaporizer bombs? It only costs 10E, 200Cr and a few materials worth about 200Cr to make a 1*; say "UV spamming". Catalyzer is a boss token reward and unavailable through crafting for a reason. Sidenote from the perspective of a primary bomber: if a bomb involves placement without requiring you to be where it is placed, you are giving less competent bombers a cheap way to claim they are competent; bombing requires the user to be competent in dodging attacks and predicting enemy behavior. Bombs were once able to be placed in the same pattern as swords without the combo limit or guns without requiring reload; imagine derpbillion Nitronomes at once everywhere forever. The charge attack was originally only useful for a little more damage but everyone preferred to spam.

Of all the 5*/maxed gun lines, how many are element? Most of them. Magnus is pierce unless you go Iron Slug. How many pierce guns are there? Blitz, Plague and Callahan? How many shadow guns are there? Biohazard, Sentenza and Umbra? Magnus line is designed to fire a heavy damage bullet which nails the target; see the stun effect on Callahan. If anything happens to this line it should be to buff it somehow; Magnus line seems to be based on a high damage per hit for each bullet. Incompetent gun users would see the damage bar and think "it must be the best gun because it has the highest base damage, hurr". No. It may have more bars but that does not make it the highest damage rate gun over time; compare it to Blitz, both firing on a neutral target:

Callahan:
Basic: 131
Charge: 296

Blitz Needle:
Basic: 62 (per shot, six bullets are fired per shot meaning this value may effectively be multiplied six fold)
Charge: 121 (see above note)

Callahan may have stun but holds nothing against dat Blitz damage. Rather than make a bastard child on the Magnus line, your efforts would be best spent rebalancing the existing lines to be more practical for those who bothered to make it.

I am not telling you "this is stupid so you should give up and commit suicide", though the idea of grenades is fairly old. If you want grenades get used to Catalyzer. The element Magnus lines are unnecessary.

Bombs are charged and planted at our feet. Throwing a bomb from a safe distance isn't classed as "bombing".

A grenade might be a "bomb" in real life, but mechanicswise in the game, it isn't.