Not at all. Speaking only about the wires attached to the switches, each 3-way has one wire on the darker terminal (the 'common'), and a pair of 'travelers'. One 'common' wire is fed the always-hot wire, and the other 'common' wire feeds the light(s).

The 4-way has the two pairs of travelers attached to it; one pair on the two dark terminals, and the other pair to the two light terminals.

To eliminate one of the 3-ways, just attach the 'common' wire to one of the travelers, take the 3-way to where the 4-way is, remove the 4-way, and attach the other end of the above-mentioned traveler to the 3-way's common, and attach the two un-disturbed travelers to the 3-way's traveler terminals.

You will have one traveler not connected to anything at either end now. To be safe, cap each end with a small wirenut, but leave it for any future use.

Larry
www.fineelectricco.com