Well Lallana definitely doesn't 'create' more goals. The assist stat is arbitrary as we all know, as often its the pass prior to the assist that plays a greater role in the goal. So you have to use your judgement from watching the game. Coutinho has 'created' plenty of goals, and has 'created' plenty of chances that didnt happen to be executed (that's the other problem with the assist stat - it relies on the recipient to finish!)
I get what you're saying, but an assist stat isn't completely arbitrary. Whilst it doesn't necessarily show the whole story, the number of assists a player gets in a season is a decent starting point for looking at their creativity. Looking at the Squawka stats per 90 (which only show the league, admittedly) the two stack up as follows:
Goals Assists Chances Created Key Passes
Lallana: 0.34* 0.25* 1.59 1.34
Coutinho: 0.11 0.22 1.61* 1.39*
As you can see this basically backs up what we've both been saying - it's true that Coutinho makes (very marginally) more key passes and creates more chances in a game, but Lallana is ahead in terms of assists (again, very marginally) and goals (by a fair distance). I'm not saying that stats are the be-all and end-all but it would seem that in terms of decisive contributions Lallana is the better bet - at the moment.
P.s. I didn't include the actual image from the page because I'm a technological klutz, but here's the link if you want to dick about with it
http://www.squawka.com/comparison-matrix#premier_league/2014/2015/adam_lallana/126/126/723/36/p|premier_league/2014/2015/philippe_coutinho/126/126/2673/0/p#key_passes/assists/chances_created/goals_scored#90