When I bought my metra ticket, I simply used a credit card saved in the app. Again, I don't see why one would use the ventra balance when you can just charge the card directly but we dont need to get into that.
As for buying the ticket, I noticed that after buying the ticket, you have to "activate" the ticket once you board. I assumed that this was like validating a ticket with other train systems meaning that you are forced to "use" the ticket even if the conductor doesnt check because if he catches you with a ticket that is validated late, you get fined or at least have to pay the on-board ticket buying fee. I guess this isnt the case with metra.
Yes the whole transit system seems to be designed to be more difficult to use that it has to. My father recently had an accident and is now in rehab downtown so my mother is taking metra in as she doesnt like driving downtown. She is a senior but is forced to apply for a senior pass thru RTA which takes 3-4 weeks in order to buy a reduced fare metra ticket when they could just as easily look at ID. My father will only be in rehab for 3-4 weeks so I'm sure it will arrive just in time for her to have no more need for it.