They are definitely not useless now. Ailment removal can save many a HC character's life. Sometimes there is just too much going on to know exactly when you fall ill.
With GGG trying to ramp up difficulty in early game, a flask manager is a massive QoL at league start and new char rolls as well.
The idea of offensive and defensive flask use has always been great too, but if kept in a manager, it would be great if it were possible to have tick boxes for specific flasks and behaviors as it is not always cut and dry which categories flasks will be tossed into.