I'm a long time Prius driver... Mine is 13 years old this June. I did a lot of research before buying it, and I'm happy to say that the doom-sayers were sadly mistaken.
First, regen braking. It would be great if regenerative braking were able to recapture all the energy used when accelerating, but the amount that is captured is limited by how much current the batteries can handle while charging. Like all batteries, you can usually draw higher current than you can put back when charging. Adding supercapacitors as momentary buffers may help, but they need to be pretty big to have a significant impact. An unexpected side effect is 150K miles between brake jobs.
Second; li-ion are not created equal. There are designs that use an anode that has an extremely large surface area via nano tech. These are able to handle a couple thousand FULL DISCHARGE cycles. As mentioned above, a partial discharge does less to reduce battery life than a full discharge.
Third; most hybrids are still using NiMh, not lithium. The Ford Escape hybrid was still using one in 2012. The Escapes are lasting far in excess of 100K miles. A taxi got 500,000 miles. Mine (a Prius, remmeber?
) is at 140,000 miles and still on the original battery pack.
Last; one of the things that Tesla is doing to prolong battery life is active cooling of the batteries. They are air conditioned.
Dan