After a lot of research, I ended up undoing my contraption, and installing the car seat fully on the driver's side, using seat belt installation. The seat on the passenger's side remains with LATCH installation, which makes one seat easily transferrable, when need be. Both have their headrests folded.
I did contact Diono (canada) about it, but the reply essentially summed up to "please refer to your vehichle's owner manual."
In the end, either lower anchors or seat belt installation is equally safe, provided they're correctly installed. (That latter point is why LATCH exists: to make a safe installation easier.) The seat belts in the pacifica seem to make it easy enough to pull them all through and engage their lock.
(of course, both top tethers are securely attached behind the benches.)
Plus, they're further apart now, which results in much quieter rides! Safety of passengers goes first through safety of the driver, after all.