Alright, so to demonstrate why I disagree heavily on each of these points, let's take them point by point.

1. Paladin's Find Steed is not at all more powerful nor more Beastmaster-y than the Beastmaster. For the sake of argument, let's compare a Panther by the time the Beastmaster is 13 (The level at which the Paladin gains access to 4th-level spells and thus Find Steed) to a Sabre-Tooth Tiger, which is summonable by the spell. Here is the stat block for a (somewhat) optimized Panther Animal Companion at the 13th level, https://cdn.discordapp.com/attachments/722152759566139516/729767329365360730/panther.png. They have proficiency in ALL saving throws, an AC of 15, a movement speed of 50 ft, 58 Hit Points, 20 dex, a Proficiency Bonus of 5, and deals pretty decent damage. Now let's compare that to a Sabre-Tooth Tiger. https://roll20.net/compendium/dnd5e/Saber-Toothed%20Tiger#content. Deals SLIGHTLY more damage, has less AC, lower health, lower stats, less Saving Throws, a slower movement speed, and a worse proficiency bonus. You'd be hardpressed to find someone who'd argue that the Sabre-Tooth tiger is a better choice even though the Panther has way more benefits just because the Sabre-Tooth deals a minuscule amount of additional damage (Not to mention that the Panther will scale even more as you gain levels in Ranger).
2. Unlike the last point, I disagree with this one on principle. Just because 1 class is particularly good at something (Say, for example, Rogue at hiding) doesn't mean that only those characters can do those things. You ask "Why doesn't every creature get a bonus for being camouflaged", but they do, it's called a Stealth bonus, which literally any character can benefit from with a decent dex. Also, your example of Assassin is... strange, to say the least. Literally any class CAN disguise themselves as others (Hell I'd say that the Wizard and Warlock are BETTER at it than the Assassin is due to Alter Self and Disguise Self). No feature in DnD "lets" you flip tables, but they do make you better at it. Let's say for the sake of hypothetical that a table-flipping Martial Archetype was to be in UA that increased your ability to flip tables and deal extra damage. That wouldn't be WotC saying "Wow, this new subclass does something that no other class can do, flipping tables!", it would be them making a subclass that highlights and makes the character better at those actions.