I'm a poor roleplayer in a roleplaying light group, and I feel the same way. One of our players is on his second warlock in two campaigns. The first one was slain outright by his patron for refusing to betray the party. He has a better arrangement this time, by all accounts. No one is dipping into warlock.
Certainly, I would get bored by doing the same thing over and over. That used to be the knock against playing a fighter.
Sorta. The DM won't put the time into building that NPC that I put into building my character, and he can't run an NPC party as well as 5 players can run 5 PCs.
This is absolutely true. However if the DM DOES want to offer more of a challenge to a player they can invest some time as online for help and get ideas to do that. The DM also is NOT obligated to disclose HOW an NPC or monster did something. As a player some of the most fun encounters were ones the DM tailored to challenge our party, and most likely broke some of the rules as written. It makes a better story and is more fun.
And tastes will change over time. In the late days of 3.5, I built a focused specialist wizard that just threw orbs of force. He was unstoppable, and being unstoppable was a lot of fun until eventually it wasn't. My last 3.5 wizard focused on battlefield control.
Sure, but if that player with the sorcerer chose Subtle Spell, the most un-DPR-ish of metamagic options, for just that kind of rarely occurring scenario, are you really going to foil all that investment for your story? I hope not.
Absolutely not. However most DM's are not trying to TPK the party. They might have something really cool planned and might railroad some of the details to get to a fun point. So let the player try things, and get creative. Be willing to change your plot/plan if the PC comes up with something clever and cool, or just say, no it didn't work..... the DM is under no obligation to explain HOW everything happens and why, so if the DM doesn't want the character getting out of the cell somehow it doesn't work. Generally DM's are trying to make a fun game. If your DM is a power hungry petty jerk, find a new DM that is more fun.
Yes, it is your job to bring the adversity, while avoiding inadvertent TPKs. There is no story otherwise.
In regards to me cheating as a DM. It is most often to AVOID a TPK. As a player I generally play wizards and rogues, and do so creatively and have a main villain in the background who gathers intel. I've also played longer than many of the players so I remember things that worked in various games in the past, and sometimes I make an encounter too hard. So I try to leave an out. Also as a DM I tell the players just because you MEET a monster doesn't mean you have any chance to beat it. I also give XP for overcoming and encounter, they don't have to murder hobo everything to advance in level. Most of my cheating is basically pulling a PC's butt out of the fire because they did something stupid and it would be unsatisfying for the character to die there. Much better a heroic death doing something memorable.
Or it could just mean that the player has chosen to fill a particular role in the party. You could have one caster who skews toward battlefield control and another who specializes in ranged attack spells, cantrips included, a third who focuses on AOE stuff, a fourth who mostly does buffs. Or one of your casters might split his attention between any two of those areas of focus. Over many levels, an odds and sods adventuring party can morph into a killing machine. In 4e, it started that way. The 4e adventuring party was a combat unit. The default construct was a leader, a controller, a defender and two strikers.
Never played 4e enough to know much about the system. It didn't feel like D&D to me. The few times I played it it WAS fun, but not the type of fun I was looking for. That said players often design a character for a certain role and that is ok. The DM has many options to challenge the players, and if they are not creative enough they can ask for help and ideas online and get tons of good advice. Best advice I can give is that the DM does not follow the rules as written and makes stuff up on the fly and is not held prisoner to the dice, but rather guides a collaborative story that is fun and satisfying for all the players, and in my opinion "cheating" as the DM makes that more possible.
A DM could just nerf a EB blaster for a certain encounter, hopefully a special one, like the BBEG has a special shield spell that works well against EB. It would be BORING to nerf the EB player ALL THE TIME for both the DM and the player, but having a few enemies that can somehow get around the powerful EB would be fun for both, but should be used sparingly so that it is still COOL.