行{い}ける vs. いける
When a common word that is usually written using kanji is written in kana, you can be 99% sure that it is being used for its "new" and/or colloquial (sometimes slangy) meaning.
So, 「行ける」 means "to be able to go", but 「いける」 means something else. What does it mean, then? Let us quote from デジタル大辞泉.
動{どう}カ下一{しもいち}]《行{い}くことができる意{い}から》
1 相当{そうとう}にうまくできる。「歌{うた}だけでなく、踊{おど}りも―・ける」
2 相当の量{りょう}の酒{さけ}が飲{の}める。「なかなか―・ける口{くち}だ」
3 飲食物{いんしょくぶつ}の味{あじ}がよく、おいしい。いただける。「ここの料理{りょうり}はちょっと―・ける」
That briefly translates to:
1 To be able to perform quite well
2 To be able to drink in large quantities
3 To taste good. Tasty, delicious.
So, the word has very positive meanings.
「戦術{せんじゅつ}と戦闘{せんとう}どっちもいける奴{やつ}には勝{か}てない。」
thus means:
"It is hard to beat a guy who is very good at both strategy and (actual) fighting."