Jack Slugger's stats: .200/.330/.450
Mickey Slapper's stats: .300/.330/.450
In your opinion Mickey Slapper is the better player. In my opinion they are equal.
Since they both have the same OBP and Mickey Slapper has a better Batting Average we can determine that Mickey Slapper gets more hits but Jack Slugger gets more walks or HBPs. Hits are better than walks. So right now it looks like Mickey Slapper is the better hitter. This is the case you are making, which is correct but incomplete.
The aspect you are not considering is this: Since you are giving more hits to Mickey Slapper you are also giving him more Total Bases (singles grant 1 TB while walks do not count as Total Bases). Since you are giving him more Total Bases his SLG should go up above the .450 mark we have quoted but it doesn't (SLG=TBs/ABs). Since we know his SLG remained at .450 despite the extra Total Bases from base hits we can conclude that Mickey Slapper must be losing Total Bases somewhere else (we know he has the same Total Bases as Jack Slugger or else they would have different SLG rates). The answer is that Mickey Slapper is getting fewer Total Bases per hit -- he is hitting singles instead of the more valuable doubles and home runs. Every time you give him a single instead of a walk you have to turn one of his doubles into a single (roughly speaking, because you are also giving him an extra AB because walks don't count as ABs). Or for every three hits instead of walks you have to turn one of his home runs into a single. Essentially, to turn a walk into a single you have to also turn an extra-base hit into a single. Otherwise the SLG will change. That is the tradeoff -- if you want your OBP to be driven by hits instead of walks you have to sacrifice your doubles and home runs.
This also means that even though Jack Slugger had fewer hits he still had the same number of Total Bases -- which means that Jack Slugger got a lot more extra base hits than Mickey Slapper did.
While a .300/.330/.450 line looks better on paper than a .200/.330/.450 line it is merely a mirage. Both lines show players who are equally productive in different ways. It is just another way to show that batting average is a stat that makes no useful or practical difference on the field.
In the end they are both contributing to the same degree to their teams' scoring chances. Mickey Slapper contributes with singles and doubles, while Jack Slugger contributes with walks, doubles and home runs. Both make outs at the same rate. Both contribute the same Total Bases. Their overall contribution is exactly the same in the end.