Though the fee is also relative to how long the ASP has to provide captial for your VTXO.

For example, if the ASP provided an ARK with a 1 year sweep time, a user planning to self custody their funds for at least a year would join the tree, wait till maybe two weeks till ASP can sweep, then redeem to a new tree. This way they would only pay interest for 2 weeks of time. 

Its important to note that all the users participating in these ARKs would be doing so because they believe the net fees they would have to pay to be in the ARK would still be cheaper than standard self-custody through an onchain transaction fee. This would likely only be true for small-medium amounts so its unlikely any very large amounts would ever participate in these ARKs.

toyota_corolla0

bitcoin

Is Self Custodial Bitcoin Possible Outside of the Main Chain?

So holding in an ASP would incur a fee relative to the amount held there, slowly bleeding away your holdings. That seems at adds with wanting to hold a lot of funds for a long period. 