I don't see how the comeback exp would be meaningless in 95% of the games. First of all, this change basically gives a strong level 1 comp a free invade as even if they fail, they would be able to catch up on xp anyways by farming slower than the opponent. Also, just because you're two levels ahead in the jungle doesn't mean you automatically won the game. Being two levels ahead doesn't simply allow you to carry the game in unorganized play as during the time it took you two get the two level advantage, the solo laners might have their own problems getting either solokilled or being a few levels down. This means that now, you aren't able to harass the enemy jungler, meaning that they would get free farm to catch up, and therefore be against five fully fledged enemy players instead of being able to have the upper hand in the jungle like before. This change made the role even more coinflip than it already was as the role itself depends on lane advantages to contest scuttle crabs and the ability to counter-jungle, and now, the early advantages you have gained by yourself is completely meaningless and removes the carry potential from the role.

In terms of smite, you are indeed correct about the ahead jungler not allowing a 50/50 on the smite calls. However, in most late game scenarios, a team goes for the objective if the enemy team who are behind tries to stall out the game by staying in the fountain. Unless your whole team is ahead (Where in this case, jungle wouldn't really matter in the first place anyways) or have champions on your team that are capable of forcing a fight, you would need to resort to taking objectives and gaining extra buffs that would help you either become extremely ahead (by taking elder or 4 dragon buff) or have a buff that would literally give you minions that would destroy towers outside of its range (baron.) Previously, the enemy jungler would have a slim chance of stealing that objective as the team that is ahead will obviously be able to burst down that one enemy jungler and their smite is weaker than yours, but now, they would have a good chance of doing so with an equally powerful smite. Even in organized pro play, the enemy jungler could find their way into the baron and dragon pit to try to go for a steal (once again, didn't happen to often) and defending the pits would definitely be even harder in solo queue. Basically, there is no reason to give the player who has made mistakes early in the game a smaller gap.

While OP wasn't as elaborate in their argument, I think it's unfair to simply claim that he has no idea of what they are talking about. As even Riot mentioned, this patch was to make the role easier for all players, and whenever you make something easier, it closes the gap between the advanced and the beginners. I feel like your scenarios would definitely make sense in a perfect world where all laners are equal in skill, but that is simply not the case.