Road bike tyre impossible to get off
Road tubeless generally should have tighter tolerances but there is no single standard so the target measurement may differ between manufacturers leading to potentially problematic rim/tire combination. Furthermore, tubeless systems that are designed to be run at high pressure (i.e., road) require beads that stretch very little, otherwise bead could become dislodged under pressure leading to a catastrophic deflation event. The rigid bead can further exacerbate issues associated with  tire/rim mismatches.

That said, most tubeless compatible rims will also have a deep center channel, which is intended to be used when mounting the tire and when removing the tire.  Once you have the bead in the center channel this should give you slack to get part of the bead over the rim.

When removing a tubeless tire go around the rim dislodging the bead into the channel.  You will often hear a load "thwack" as you dislodge the bead into the channel due to the release of tension caused by the tight high fit needed for an air tight seal. This is the critical step that may require a reasonable amount of hand strength. As you work around the wheel also check on areas you have already dislodged into the channel as the bead can work its way back out of the channel and back to the bead seat.  

Once all of the beads on both sides of the tire are in the channel you should have enough slack to get a tire lever under the bead and to dislodge the bead over the rim.  You may need a second lever, one to hold a dislodged bead in place, the second to continue dislodging more tire bead over the rim.

If the tire starts becomes incredibly tight while dislodging the bead, check that the remaining tire bead is properly nested in the channel  and has not worked its way out of the channel.

Finally, if you are running tubeless tires on a non-tubeless rim, older varieties of rim (i.e., more than 5-10 years) may have no or an insufficiently deep center channel for the easy mounting/dismounting of tubeless  tires. In this case I would suggest forgoing the tubeless tire and sticking to regular clincher tires, most manufacturers still offer both construction types.