Welcome to this forum. I started out with karate, went on to Kendo and I quit both MA's since I have a view upon fighthing and competing that is somewhat similar to yours. This is why I stick to Aikido. Been doing it for about 3 years now. I just love it. What I can tell you is this: I can only practice once a week except for a two or three seminars a year where I get three to five days of practice at once. It's not as much as I could wish, but it far far better than NOT going. It teaches me a valuable lesson when I see new members quickly surpass me in skill since they can practise 4 or 5 days a week, but I'm a dad and I have a job to take care of. These things takes time, and I must fit Aikido in as best I can. It's not ideal, but it's still great.
So yes! once a week can be great - as long as you don't expect to progress as fast as others. On the other hand, one thing you can be sure of in Aikido is, that there will ALWAYS be someone who can teach you something new.
I hope you'll give it a try, and that you will enjoy it as much as I do.