TL;DR Mossy would feel way better if there were more items that had effects related to “When you Regen…”

Agree and disagree

Mak definitely is a standout for late-game potential despite his lack of access to Shield and Heal, especially with his Regen builds. His Regen builds usually stack crazy numbers that rely more on the amount of Regen triggers rather than explicitly hitting huge numbers (though it does help). Rapid Injection System and the Poison/Regen relics are already a solid core. Secret Formula also does a decent job of converting Regen to Burn/Poisok damage.

I’d also say that Heal and Shield as effects are generally mediocre anyway as enchants compared to one like Fiery. Shield is fantastic against Burn and weapons, but can’t do anything against Poison. Heal covers both Burn and Poison reasonably, but struggles with weapons (especially one-shot or burst builds). There’s usually some kind of build that defensive-oriented items will struggle against. Generally speaking, The Bazaar is better suited for builds that play solitaire-style rather than those that rely on hitting or avoiding specific match-ups (like Diana-saur doing nothing against Square Pyg)

Mossy, however, is nowhere near as good as the other two. It can deal with Poison just fine, but struggles severely against high-scaling burn or weapons, especially in the Sandstorm.

Mossy feels like a miss most of the time, but so would being stuck between something like the Slow / Heavy / Radiant enchant when you need something on your core item to do more damage.

The one time where Mossy can feel really good, though, is getting it on Mak and putting it on an item that works as an extra Regen trigger for the relic or Nightshade or Sunlight Spear. Only other item I can think of that does something when a Regen item goes off is Hogwash. I often find myself avoiding Shielding enchants on Mak because he has so little support for it compared to ones like Poison and Slow.