That depends upon which version of “efficacious” one is looking at. Both are equal in imparting grace.
The OF is noted as being better at teaching the faith when properly implemented (an extra reading, better organization of the readings into themes from the church teaching). It’s also noted as being better able to adjust for cultural differences.
The EF is noted as being better at promoting reverence. (But many older priests remember otherwise when it was the only form in use in the Roman Rite.) It’s more consistent in presentation. It’s normally more able to trigger sense memories (because the use of bells and incenses is optional in the OF).
The church has multiple needs - one of them (identified by the V II council fathers) was improving catechesis, especially of adult faithful. The extra reading for sunday masses and holyday masses was part of that; the alignment into thematic units of the lectionary was another part of that. The acknowledgement that most people don’t participate in the office of the hours was part of why many of the readings for the breviary are now also in the lectionary (tho’ not normally on the same day) for the Mass. Likewise, the realization that most of the faithful don’t go to daily mass is why the lectionary has a different cycle for the weekdays from the sundays/holydays. The sunday cycle is, without a doubt, an acknowledgement of the western society’s changes in lifestyle.
So, yes, in some ways it can be said to be clearly better; in others, worse. But it’s been a blessing for many - and for the rest, the EF is still available, as are the Eastern Catholic Churches.