You don't need to miss being able to see the old monsters, you can see the old basic rules monsters under either the free Basic Rules (2014) source under sources, or by clicking monsters under the game rules tab, and filtering by source, when you filter by source you can filter by Basic Rules (2014), Player's Handbook (2014), D&D Free Rules (2024), or Player's Handbook (2024). The only thing that is broken at the moment is the Player's Handbook (2024) only shows creatures that are in that book and not in the D&D Free Rules.

It's likely called Rend in the Black Bear stat block because it isn't specified to be a claw attack or a bite attack, it just says Melee attack roll. It could feasibly be any attack a black bear could make that dealt slashing damage.

In the Brown Bear it is specified to be a Claw attack and a Bite attack, because they have separate effects. They deal different damage, and Claw has a secondary feature. This is likely also another reason for it to be Claw and not Rend, because they have different rules.

There were actually three bears in the Basic Rules (2014) as it included the Polar Bear. I suppose there are this many because players, and DM's want some monsters to be powerscaled. As a DM I would rather make a combat encounter with one big bear and a few smaller bears, i.e. maybe a polar bear and 4 black bears, to spice it up. If I was playing a Circle of the Moon Druid, I would like to have my bear's wildshape become more powerful as I gained access to higher CR creatures.

The d4 claw attack on the large bear is a glitch, right?

Looks like they scaled Beast damage down across the board so that Moon Druids do not outpace other classes with regards to offensive output.

Also looks like they missed adding Perception Expertise when they removed Keen Smell (as opposed to what they did for most of the other Beasts I've looked at).

A few trade offs from 2014 version. The auto prone on the claw is quite a buff though. 

Yeah, I mean look at it! Those 6 claws on that paw; 🐾 enormous, should be 1d6 minimum 😂

rip bears

I mean, it still straight up kills a commoner no matter the roll.

no, now it knocks prone which is so much better

So they took out Keen Smell, lowered the HP by 12, lowered both STR and CON, and lowered the damage from the claw attack. And in return the claws got an auto prone effect and DEX got a boost.

This works for an interior brown bear but not a Coastal one as they are much closer to polar bears in size. For a Coastal id up its Ac to 12, HP to 30 (4d10+8), Str to 18 +4, and either give it two Rend attacks being 8 (1d8+4) or keep the bite as 8 (1d8+4) and the claw as 7 (1d6+4).