That's a rubbish objection. Attack the message - not the messenger. I cited the paper so that you can verify that the figures I provided are correct. Furthermore, new rental apartments already are excluded from rent control so rent control can't be the reason so few apartments of any type is being built. 20-30 years is for the most desirable areas of Stockholm (Gamla stan) and is not the median queuing time.
Six to seven years is nothing compared to Sweden where you can have queues about 20-30 years easily for the big cities. My GF have 12 years in the queue and she can get a decent apartment in the outskirts of Stockholm but that is about it.
There are special housing for elderly, which is a bit shorter in the queues but still very long.