He’s not a great fielding first baseman - he’s passable but was a liability compared to Mike Napoli who he replaced. And Napoli is good but certainly not great. First base is where you put anyone who’s a big bat but a lousy fielder - they don’t have to throw, they don’t have to field much, and they don’t need range.
It’s likely his career would not have been what it was. Certainly he would have had “a career” in the sense that of course he would have appeared in a number of Major LEague Baseball games, but it doesn’t seem likely a person of his abilities would have sustained his hitting excellence as long as he would have were it not for the DH rule.
As to why he started a few games at first base in the World Series, I think it is… well, I think you must know why there is a difference between a guy starting three games in the World Series out of necessity versus the demand of starting 150 or so games throughout the regular season.
I get the sense people just make stuff up because it’s cool to not like the DH. Here’s one of them.
Seriously, what the hell is NATURAL about that? There isn’t anything “natural” about baseball. It’s a purely artificial enterprise set up why wholly artificial rules. There’s nothing “Natural” about using an 8-man lineup, or a 9-man lineup. (If you want a specific problem with your idea, an obvious one is that you’d change the standards for the number of plate appearances a batter gets and thus really warp season totals and statistical standards.)
Well, I say there is; the evolutionarily-derived phenomenon that pitchers can’t hit at a level suited to top-level professional baseball. That circumstance, in my opinion, suggests the DH as a logical and elegant solution.
Yep. So? 
Isn’t the whole point of this thread to sneer at the Designated Hitler?
That is how I see it!
Why? Football originally had limited substitution just like baseball. You come out of the game, you can’t go back in. Even into the 60s college football still didn’t have unlimited substitution. If football can be changed for the “better” why can’t baseball as well? You may not like the rule, but it is no more inherently against the way it is “supposed” to be played than is unlimited substitution in football.
I’d say the adoption of unlimited substitution more radically changed football than did the DH rule in baseball. For one thing, I don’t think many of the 300+ linemen could play the whole game. If you still had limited substitution, you’d have much lighter players, and I suspect as a result, much less use of HGH and steroids.