Who is the worst world champion?

in terms of skill

Probably those crowned by FIDE alone between 1993 and 2006.

Now, amongst those widely accepted by the chess community, it's Steinitz most likely, although I wouldn't use "worst" but less talented. Both Zukertort and Tschigorin seemed better at chess (as we understand it today), but Steinitz's discoveries –regarding positional play– proved too much for both.

Some argue that Euwe deserved the distinction, although not because of his lack of talent but that he was crowned after facing a "weakened" opposition. Indeed, but Euwe was an amateur player, not a professional devoted only to chess, meaning he gave a handicap throughout all his chess career.

And none of the current top 100 has made the contribution to chess understanding and theory as Steinitz did. Not even close.

To give an idea, nowadays understanding of chess dynamism and ultra dynamism comes from the games and writings of over a dozen players over half a century, while Steinitz's writings took him less than a decade.

https://www.chess.com/article/view/behold-steinitz-the-austrian-morphy

https://www.chess.com/article/view/steinitz-changes-the-chess-world

https://www.chess.com/article/view/steinitz-the-official-world-chess-champion

@kindaspongey Yeah, but Silman doesn't mention Steinitz's dogmatic approach to some positions, meaning adding too much value to his own principles.

For example, if he could build a strong center at the cost of his own King's security, he valued more the inherent defensive capabilities of such center disregarding the tempos involved in securing his own position. Or allowing strong initiatives to his rivals as long as he wasn't forced to concede structural weaknesses, as he believed that without them his game could be held.

Such defects in the understanding of activity, coordination, and tempos can not be found in later World Champions, Euwe included (who really played Steinitz–like), and is believed that had more to do with Steinitz trying to demonstrate the validity of his "universal principles" than to solve properly the position in front of him.

Yes great post. 

Did later world champions have somewhat more to look at and learn from?

Indeed. Whereas by intuition or better understanding, both Lasker and Capablanca valued activity above positional concessions. Alekhine realized that it wasn't about preventing the rival from running, but to finish first.

Although Bronstein didn't win the crown, he demonstrated that it was possible to play "different". His –and other soviet players– ideas about dynamism (and ultra dynamism) can be seen in several of Tal's games:

(As a curiosity, Tal didn't want to analyze that game because he said his annotations would be wrong.)

In any case, after 1972 it was widely accepted that it was possible to play and –somewhat– properly conduct such games: Leading the game into multiple and constantly changing objectives –for both sides– with a degree of confidence in the outcome.

and the ability to look back on the history of most of the last half of the 19th century?

myself

Nope. It has to do with "understanding" what can be played successfully and what cannot.

For instance, according to Steinitz's principles, it is wrong to leave holes in the position as such play must lose against correct play. But then we have all those Open Sicilian variations where Black moves ...Pe7–e5, leaving a "weak" d5–square. When a theory fails to predict a single outcome (regardless of the times it was right), that theory is wrong and must be discarded.

Back in Bronstein and Tal's times, some people said both played "wrong" chess and succeded only because of their tactical strength ("combinative imagination" and "positional sacrifices" were often used). It wasn't believed that such approaching followed "rules and guidelines" too, therefore couldn't be explained nor taught.

Besides, it wasn't necessary to develop a self–learning AI to realize Steinitz's ideas had too many holes. Check the dates in these two games, annotated by Kasparov:

Then, it's not that Steinitz was completely wrong with his ideas, but when not accepting that they explained some positions but not all of them. At some point, his own prestige seemed to be more important to him than the needs of the position. So, if the question is "who was the less skilled of them all?", Steinitz has to win the cake because of his dogmatic approach to the game.

I would say Smyslov. I've never heard anyone say, "I need to study those Smyslov games. He brought a new perspective to the game. Look at all of the tons of contributions he has made to advance chess."

Furthermore, when I read My Great Predecessors by Kasparov, Smysolv seems a bit unimportant compared to the other World Champions.

You feel that you have some way of knowing that Lasker was not aided in his understanding by knowledge of what had gone on during most of the last half of the 19th century?

I think is you should give credit where credit is due. Just because of Ruy López publishing a book in 1561, doesn't mean everyone thereafter should give credit to him when winning after 1.e4 e5 2.Nf3 Nc6 3.Bb5. Incidentally, we don't even know if Ruy López invented that opening.

What we do know is that all World Champions, but Steinitz, valued activity whether by knowledge or intuition, while Steinitz –at some point– was more interested in proving his writings were correct.

you obviously.. duh!

Not talking about 1561 Ruy Lopez. I am talking about the substantial amount of match and tournament practice that took place during most of the last half of the 19th century. You have a reason to believe that Lasker and others were not aided by that?

Knowledge that would not have been available to someone who was devising his ideas while actually playing during much of the last half of the 19th century?

"... The analytical work of Steinitz extends over thirty years and is very valuable. In the Field, in the Tribune, in his publication International Chess Magazine and in his book Modern Chess Instructor, one may find his penetrating and profound analysis. ... Now let us turn back to Steinitz and demonstrate his revolutionary achievement from his history and from his writings. ..." - Emanuel Lasker (~1925)

Lasker was able to read that stuff. Steinitz was kinda busy writing it.