Not always but they are not as easy to defeat as the hornets. I recommend to get the iron shivs (4 attacks instead of only 1) to defeat them quick enough so they can't stun you. Or use magic against them (probably fire, not sure tho).
The slimes are highly magic resistant in general, the only magic that works on them effectively is Ice Magic. Although, if you invested properly as a mage, you can one shot them with an ice spell or possibly with the combo follow up spell if your stats are less optimal. Otherwise, if you're not a mage or do not have any ice spells, then melee is effective as you noted.
If you lack both melee and magic combat abilities, or the raw stats and gear to support a simple attack build, and if you don't mind bedding goblins, you can impregnate 100 goblins to earn the Goblin Breeder title that awards +5 VP, increases your fertility in scenes involving goblins, and grants you the Goblin Punch, which is a powerful attack that scales solely off the number of goblins you have fathered. As long as the enemy is not highly resistant or immune to blunt damage, the Goblin Punch could have one-shot potential if you father enough children, although the ability will eventually receive a damage cap. But for now, you could theoretically decimate any enemy with that attack at the moment.
The move does require 10 TP to use, but if you make or find and wear a Silk Scarf, it will allow you to retain your TP between fights. Just wear said scarf, go slay some rats to build up your TP, and then use it fuel your one punch impersonation on slimes, werewolves, bandits, or whatever else you want or need to destroy.
As a final bonus note, slimes can rarely drop a slime core item which will turn into a pet slime if you use it. The pet slime's default name is Jelly Bean, but you can rename them when you first summon them.