...Those are worse examples? The first two at least.
For those who don't know, the tiers in this website are Uber, Overused/OU, Underused/UU, Rarely Used/RU, Never Used/NU, and PU, which is a pun on pokemon which just stink. This is largely determined by their popularity in pokemon showdown matches the tier - more popular pokemon are assumed to be better. There's also the BL tiers, which are pokemon that are too good for their tier but not popular in the next tier up. If a Pokemon isn't even popular in PU, it's considered Untiered.
Beedrill is so bad that it's in the Untiered, but the much more aggressively statted Orbeetle is so good that it's in the... Untiered!
Raticate is so shite that it's in the untiered, but the much more defensively built greedent managed to reach the lofty heights of... Untiered!
These groups are easy comparisons to make, but the problem is that they're so shite by default that being half-decent is an unironically good thing.
As for the birds, that's a better example but still pretty iffy. Over time, the birds have generally improved in quality. Staraptor is UUBL, and has been UUBL for it's entire existence. Pidgeot was bottom-tier trash when it started, and the highest it's ever been is NU. More recently, we've had Talonflame, which was Ubers in it's time, and Corviknight, which is comfortably OU, but sandwiched between them is Toucannon who also came out Untiered.
It's not that they're getting squeezed out by new hotness, its that they were never good in the first place, and these newer ones occasionally fluke to greatest but are mostly just decent at best.
Also: Learn to thumbnail, mate. it's obnoxiously huge on PC.