To stop WFH because rules not applied equally

[FoxtrotOscarFoxtrotOscar]

Have had a shit day at work.
I started a new FT job in my very large organisation this time last year.
We can WFH two days per week and three days in the office.
If we take a day off, WFH is reduced accordingly.

The WFH and planning calendar (with various tasks) has been drawn up by one of my counterparts since before I arrived. It should have been done by our senior colleague but she is inept beyond belief.

Anyway, this suits my colleague down to the ground and she has been giving herself a lovely working regime and choice of tasks and recently started allocating herself three days WFH (1 full day and 2 half-days) twice a month to work around her childcare arrangements.
However, when I have taken a day's leave, she's quick to apply the rules to me to ensure I'm in 3 days a week.

This inequality got me so worked up that I discussed it with my boss.
He has now taken the planning away from this person and given it to the inept colleague. However, my boss announced yesterday that he would make an occasional exception but didn't want to see a "systematic" pattern. This is utter BS and contrary to our organisation's rules.

I am now seriously considering going into the office 5 days a week because the WFH arrangements have angered me so much and I don't want to be part of it.

Am I cutting my nose off to spite my face?

I also had a look at job vacancies today in other areas of the organisation but there's nothing I can apply for at the moment.

Someone talk some sense to me, please. I am so pissed off.

A half a day is still a pain in the butt. You have to go into the office then come home in your lunch break or the other way around and settle in to the other location quickly and get on with work. If anything I hate any half days I have to do.

Dunno how it benefits you though?

It's a pain going in??

I think not only are you cutting your nose off to spite your face but your actions are likely to contribute to a negative change in workplace culture overall so your team are going to suffer because of you too.

Unless I'm missing something: Colleague A stepped in for the incompetent senior Colleague B and gave herself 3 whole or partial WFH days a week while only allowing others 2. Now Boss has stripped Colleague A of this responsibility after you pointed out the issue, and given it back to Colleague B - so the original problem is resolved? In that case I'd give Colleague B a chance and now you know that if there are still issues, your boss is likely to be responsive.

I'm not sure what the issue is with Boss saying 'he would make an occasional exception but didn't want to see a "systematic" pattern' (I'm assuming that's to the 3-days-in rule). Do you want him to say up front that he won't make any exceptions? FWIW, in my experience (WFH since 2011) allowing an occasional extra WFH day for a specific reason can be a good thing for employees as long as someone responsible is making sure it isn;t abused. In any case - I don't think anyone will really notice if you come in 5 days a week, since the policy is only about limiting WFH days - if people notice at all they'll likely just think it suits you to come in.

At our workplace we have a standard four day working week. The WFH rule is three in, one at home. I work two and two because I have a health issue that is exacerbated by being tired/run down. Some people probably think I get away with something they don't but they have no idea why I have the pattern I do. Same as you have no idea why she's able to do what she does.
If I was you, rather than make myself miserable by going into the office every day, I'd stay away as much as possible. You obviously have a chip on your shoulder and don't like your colleagues very much.