I agree with you that if characters weren't ordered within tiers it would be a good idea to have fewer tiers. However, since they are ordered within tiers there's much less need to have more tiers. You could put, say, Marth at the top of high tier and Lucario at the bottom, for instance. I think that having too many tiers makes it hard to give a description of how strong the characters in the tier are, and what they can do, and such. Having too few tiers would be problematic as well, though. I think somewhere around 6-8 is ideal for Smash 4.
I don't like your tier descriptions though. Having two top tiers is fine, since there are clear differences between, say, Diddy Kong and Bayonetta. Having two high tiers is more questionable, although I could see having characters like Marth, Mega Man, and Meta Knight in the higher one and characters like Ness, Lucario, and Greninja in the other one. I think mid tier actually needs three tiers, since there are so many characters that fall somewhere into mid-tier. I'd say there are 25-30 characters in some sort of "mid tier", around half of the roster. I think having two low-tiers and one bottom tier is too much. At this point in time, I question the need to even have a bottom tier. Yes, Jigglypuff, Ganondorf, and Zelda have some serious flaws, but they do have the occasional results and can do reasonably well. Also, many characters that were traditionally seen as "low tier" have proven themselves and should probably be low-mid instead, or maybe even mid. Characters like Palutena, Shulk (who ZeRo put in "upper"), Roy, even Charizard.
So, a new tier list could look like this:
Top + (name pending, around 4-6 characters)
Top - (name pending, around 4-6 characters)
High (around 9-13 characters)
High-Mid (around (9-13 characters)
Mid (around 7-10 characters)
Low-Mid (around 7-12 characters)
Low (around 3-12 characters)
I'm still not really sure that there's a need to divide top into two tiers. If, say, Bayonetta is #10 and Diddy Kong is #1, it's pretty clear who is better anyway.
The 4BR has the same amount of tiers, just for example. S and A are Top, B and C are High, D and E are Mid, F and G are Low and H is the bottom tier. It's not uncommon for tier lists to have high and low and high sections of a tier, and there's a relatively simple explanation for this. The reason why there are a high and low top tier, for example, is while all the characters within that specific range can all theoretically have the best shot at winning tournaments, have similar certain characters have better qualities that make them a little better. In turn, you can't rank them lower into the high tier, because they are noticeably better than those characters too. Sure, you can say "why bother", but it's mainly for visual pleasure, as well as ease of ordering.
For example, lets take Fox and ZSS on the 4BR Tier List, Fox at the bottom of the S tier, and ZSS at the top of the A tier. S and A tier are considered both Top Tier, but why have they been separated? Let's look into the characters a bit.
Both characters are actually relatively similar on paper; both have great mobility, both have great combo games, both with plenty of setups into their combos, both are fastfallers and are light, and have both been proven on many occasion to win tournaments, and place within the top 5 of top level tournament play.
However, there is a notable difference that seperates these two, and it's their relative risk, and disadvantage state. In order to use ZSS correctly, you must effectively space a fair amount of her moves in the neutral in order for them to be effective. Nair and Zair are two examples. Fox doesn't have this problem, and his neutral is actually a whole lot safer and easier to use, due to his quicker, low lag, low committal options in Utilt, Bair and Ftilt. What's more, ZSS's disadvantage state is a lot bigger/easier to exploit than Fox's. Both characters get combo'd relatively easy, but that's not the area I am going into. ZSS relies on her grab a lot for some of her most deadly setups. Should ZSS miss a grab, she is left wide open, somewhere Fox does not have to worry about, and actually gets his reward from some of his spacing/neutral tools. In effect, ZSS is also much harder to play consistently than Fox, which separates them in the top tier. Both characters are certainly top tier, but this is an example of how we can group characters together even further in specific ranges, once again, going back to my point of it being far easier to fine tune a tier list with more tiers.
I also still disagree with your opinion on the bottom tier; we still need one. Yes, while characters such as Ganondorf and Jigglypuff can get results on occasion, it all depends on each tournament, and by that I mean that it depends on who they encounter in tournament. These characters have some of the most abysmal matchups in the entire game (Ganon v Sheik/virtually any character with a usable projectile zoning game, Puff v Cloud/anybody with a disjoint etc). If these characters don't encounter any of these bad matchups, then yes, they still do stand a chance, but the reason they are considered bottom tier, is because characters that are considered a little higher in low tier don't have these abysmal flaws, such as Doc and Roy, or have a notable niche against certain characters, which the bottom tiers lack. What I am effectively trying to say, is that yes, while Ganon, Puff, Zelda etc can occasionally get results, like Roy, Falco etc, they do not have as severe flaws, or just don't have a reason to be used over another similar character. Theoretically, they aren't that different to them, but the differences are noticeable.
I also want to point out that Bottom Tier is by no means as bad as it is in comparison to past games. The characters are still usable. Lets presend tiers are ordered in numerical value, with 10 being best, and 1 being worst. As an example, Brawl's best character, Meta Knight, would clearly be a 10, and Brawl's worst character, Ganon, would be a 1 or a 2, no doubt. Let's put that spin on Smash 4. Because of the overall balance of the game, the best character, Diddy, could be considered perhaps only a 9, while the worst characters, such as Ganon, Zelda and Puff, could be considered at 4 or a 3.5. Bottom tier in this game is far more viable than past bottom tiers, and it's thanks to the overall game balance.
As a final point, I want to stress that
there should be no Jigglypuff tier. NO character in this game is flawed enough to be in a tier of their own, even Jigglypuff.