OK so a little more thought on this, and, thought I really like the idea of Burdens, I do not like the way they are being implemented. I do not think these should be features you can take as you are leveling up. I think burdens should be RP elements you select at character creation, and get "gift" (Bonus, boon, whatever) for doing so.
A couple of Examples...
>>> You can select a boon and along with it, a burden (so, remove the +2 attribute modifier). If you like one of the boons, you can take it and along with it, get a burden (you can, I supposed, take a feat as well, but I think feats tend to be a little more "powerful"). So it's an even exchange. You get a boon and along with it a burden.
>>>Or you have the option to take a burden, and get a bonus +1 to whatever attribute you want (with possible limits on maximums). That's seems fair....want and extra attribute point? Take a burden.
For my "Grimdark" game, I have a list of burdens that can be rolled for at random, and it's and completely optional if you want to roll on that table. If you do decide to roll on the table, you get to add +1 to any attribute you choose as long as it doesn't exceed 18. In exchange, you get a burden.
I just feel like those should be part of character creation, not using and ASI. Of course, as the rules state, they are optional, so I suppose, "use as you will"