These antitank weapons came available for Finnish troops in the last minute, and you're partly correct. Against the frontal (and sloped) armour of T34/85, Panzerfaust was pretty useless (as I've read from several accounts). Same goes for ISU-152 and IS-tanks that the Finns faced in the summer 1944. However armour is slightly weaker on the sides and the rear, where an experienced soldier would like to score a hit. Or you just sit tight and let it go. Luckily there were also other (better) AT weapons available.