Viper may be the most under utilized Agent in all of Valorant.
Valorant players simply don't pick Viper as much as other Agents. That is a fact. Her abilities and skills are not the problem. The issue is that it took too long for Riot Games to make her useful.
When Valorant released, Viper had plenty of potential. That potential was finally capitalized on, but other Agents also received changes that continued to make them more viable.
Valorant players are still finding reasons as to why Viper isn't picked more. Recently, a discussion on Reddit brought attention to the fact that Viper's decay does not give the player any tallies in the assist column.
Viper's decay doesn't count as an assist in Valorant
Assists aren't the most important stat in Valorant, but they certainly show when someone is being a team player. Someone with a high number of assists may not be getting kills, but are clearly being a supporting player and setting up teammates for success.
Viper can truly help a team with her abilities, but does not get the recognition of the assist stat. Several Agents are given assist points based on their abilities. Examples of that are Cypher getting an assist when a teammate eliminates a player in the Trap Wire and when a player revived or healed by Sage gets a kill, Sage gets an assist.
Three of Viper's abilities deal an effect known as Decay. Poison Cloud, Toxic Screen, and the Ultimate, Viper's Pit, chip away at enemy health when they are within the Poison.
When that Decay is active and the opponent hasn't regenerated the health, Viper does not receive an assist if that player is eliminated by a teammate. When compared to other Valorant Agents, it is an awful oversight.
Viper can realistically be an Agent that locks down sites and can set up pushes with screens and smokes. No one seems to care though, due to the lack of attention given by Riot Games.
It is extremely unfortunate to see such a unique Agent be cast aside so easily. This is just another reason among many as to why Viper sees hardly any action in the competitive matches of Valorant.