Yes. Last I checked, switching out a Disaster SR Assault SLV20 for an SSR is about a 2-3% damage loss for a maxed monogrid player (me). That loss increases the more assault skill you remove, but is mitigated by running a team with elemental advantage. However, the rainbow SSR grid strategy still relies on skill leveling the SSRs. It's more efficient in the long-term, but a monogrid player is unlikely to build 6 teams with skill-leveled SRs. They'll build 1-2 teams, and then shift to skill leveling SSRs only. So the opportunity cost is actually pretty minimal in the long-term.
Building a maxed monogrid takes about 3 months, and a player can farm Disaster Assault weapons at a rate of about 2 drops per week. A monogrid team isn't particularly effective on neutral-element content until about +60% assault, or ~SLVL6 average among all 10 slots.