Above all, thank you for taking the time to answer me.
The second segment and the boss being part of the same challenge? Why not to make the whole stage part of the same challenge? It would be more difficult and challenging that way. Where do we draw the line?
People of all skill levels should be able to beat a game, and not only arcade enthusiasts that lived there. Arcades are a business, and if somebody found this (or any other) game too difficult, there's a risk that he would walk out of frustration and never play this game again, which is a loss of income for the company. A game can be difficult but manageable, offering different approaches to a single problem and not asking for a super play for every move.
Games back at that time were difficult for many reasons, many of which have been disclosed in recent interviews. Arcade games were to make more money out of you, not for intensity or anything like that. Console games were also difficult because they had short development cycles and they had to be made that way to prevent children with lots of free time to master them and beat them quickly. Those kids are now parents and have limited time to spend on games, and they should be able to play, have fun and beat those games, and not spend all their free time trying to beat that boss for the 100th time. Sometimes they didn't have feedback from players outside the development cycle, but from the game testers and developers, and they made it even more difficult! This is the story of Ninja Gaiden if I remember correctly.
Then again, modern gaming concedes this point. I'm playing Ultimate GnG right now and it is exactly what I thought it would be. You have multiple hits, respawns, several items and savestates, because that is what people demands right now. Difficulty in this series doesn't only come out as part of the artistic vision or design, but of necessity, because they are actually short games when you know what to do. From 1993 to 2006 the gaming landscape had completely changed. I concede that difficulty is part of the series' signature, but how much difficulty is needed?
One of my favourite arcade games is Radiant Silvergun. If you play it like a normal shmup it is more or less easy, but if you want to get a high score, you need to kill enemies in patterns and leave many untouched, which fills the screen with bullets thus making it harder. It is clever design and has something for everyone. It is a 1998 game and it shows the arcade school of gaming was changing to something more democratic.
To your checkpoint argument - the developers chose to divide the levels up in that way, and they are reasonably completeable that way, so there's no problem. GnG bosses are typically fairly simplistic (compared to, say, Mega Man bosses) with low health, so it's reasonable to ask the player to defeat them and the latter half of the stage in one go (which might not entirely be the case in a Mega Man game, given that series' typically sturdier bosses). Also, the spaced out checkpoints don't just serve to increase difficulty - not being thrown right back into the boss fight on death gives the player a chance to change their weapon or return to the fight with gold armor, if they need it. That said, I think the game is best played on one credit anyway - its randomness and intensity mean that it's always fun to replay - so I don't have any problem viewing the entire game as one unit; as one continuous challenge.
Ghouls 'n Ghosts allows for plenty of versatility. Look up several playthroughs on Youtube and you'll see that the game offers enough freedom to take on its challenges with a variety of different weapons (even the weaker ones) and different strategies. The game is difficult, but not oppressively so. And there are plenty of classic arcade games that are significantly harder (Ghosts 'n Goblins, Final Fight, Dodonpachi) yet that still went on to earn great success in arcades - so who's to say what really is too hard? Clearly the GnG games were not.
Yes, arcade games were made to be hard because easy games would make less money; I admitted that myself earlier. And some difficult console games were difficult because they didn't have that difficulty tested out of them - that is true. But that's completely irrelevant. Those points don't change the fact that those games are better for that. Just compare Ghouls 'n Ghosts to, say, Mega Man or Mega Man 2. The GnG games were made as arcade-level challenges intended to kick weaker players off their credits quickly; the first Mega Man games were designed as easier, milder challenges meant to be completed by players of all skill levels. The end result of that is that the Mega Man games are significantly less replayable and less intense games, with far sparser stages and plenty of "easy outs" that let even mid-tier players break the games over their knee (and incidentally, they're far less polished games, too). They respect their players far less than the GnG games.
I think what you're asking for comes across as a little distasteful. So because working adults can't or won't spend the time to learn games now, the games should lower themselves to meet their audience, rather than try to surpass what came before? The player should raise themselves to meet the game, not vice-versa - and really, arcade-style games like Ghouls 'n Ghosts are perfect for the gamer with little time because they're easily playable in short bursts. People who lack dedication can find something else to play; no one is entitled to see all a game has to offer just because they set hands on the controller (although of course there are plenty of games made with that philosophy in mind).
I can't say I care much for the initial release of Ultimate Ghosts 'n Goblins. The severe cutbacks in difficulty on the easy modes aside, I don't think the backtracking and item collecting elements fit the series especially well. Capcom and series creator Fujiwara apparently agreed, since a year later they re-released the game and included a new arcade-style mode that brings the game back in line with the previous entries (which I think is the definitive version of the game). And I don't think I'm all about Radiant Silvergun either - absolutely gorgeous aesthetics, but the scoring system is kind of tedious, and asking you to limit yourself to only killing one-third of the enemies isn't very enjoyable. I don't think I'd call it "easy" to play, either. Shmups, more than almost any other genre, are severely devalued if you choose to credit feed (you literally can't lose, and getting through the game is just a matter of time - you may as well be watching a Youtube video). That said, I think there are really great shmups that came out years later that still adhere to older, well-supported arcade design philosophies - look at Dodonpachi (1997 - not later, but close enough to RS), Ketsui and Espgaluda (2003), and Mushihimesama (2004).
