Then pay the karma afterwards.
That does literally nothing to address the issue though. Example:
My goal is to get swol, bro! Taking that Body from 5 to 6. Just completed my 5th run, and have the 30 karma needed to do so. I can A or B.
A: Spend my 30 karma now. Wait 12 game sessions before I get to use Attribute increase.
B: Wait 12 game sessions. Spend that 30 karma, that wasn't going anywhere else anyways, because I needed it for this increase.
Either way you are still waiting 11 game sessions for that upgrade you were able to afford 12 sessions ago. That is ludicrous and entirely unfun. Yes, 5e had a wait to, but waiting 1 session vs. 11 is an incredible gap.
As for those "many": I mean the repeated complaints about the new Armor system due to being unrealistic.
I personally think that is an enormous false equivalency. The training times are realistic and logical, but unfun and do not flow well with the anticipated flow of game in terms of how shadowrunners live their lives. The armor issue is unrealistic, illogical, unfun, and does not flow well with the expectation of what should happen when an individual dons gear designed to protect them from gunfire.
Not all folks can articulate their position well, and not all folks can understand anything past the literal words someone invokes. Armor system being "unrealistic" is a good, simplified way of explaining the feelings of the "many" who've criticized it, but it may not capture the exact nuances of why it is actually poorly designed.