Avira, if you notice, the criteria for bchezkas moshiach are all personal traits, whereas moshiach Vadai are all effects in the world. The first criterion of moshiach Vadai is עשה והצליח. This implies that when it says יכוף כל ישראל לילך בה ולחזק בדקה, by bchezkas moshiach- it means that he as a person did his best to influence things in that direction…. And if it is indeed successful then he’s moshiach Vadai.
The Rebbe put in the infrastructure to change the tide for world Jewry, and yes it didn’t immediately turn around, but slowly but surely The Rebbes work is paying off. And it’s still his work today, because every Lubavitcher feels The Rebbes guidance today, which is why he’s still our Rebbe… and we have what to do until we complete our mission of bringing moshiach.
A practical example is a recent Pew study which indicates that a large percentage of Jews today are in Chabad houses and programs, the closing Reform temples and expanding Chabad houses, the Reform movement turning in the direction of adding mitzvos back in to the picture etc.
Also if you only measure success by frume yidden, you will get a smaller, growing number, but if you measure success as in how many yidden are growing in Mitzvah observance, one Mitzvah at a time, and on their way up, the number is vast.
Just some things to think about