Let's do a quick math and see how profitable SLP could be. One Axie costs around 180 bucks right now, with some decent team management to get a better version so you could win without running out of stamina, you could say 200 bucks per Axie is a good average.
You need 3 of them, which makes it 600 dollars total, give or take of course. Considering the costs of high gas fee, let's say you can build a team for 750 bucks easily, sure it won't be the best but it won't be the worst neither. So, you spent 750 dollars, and now you want to earn money right?
Well, with the PVE part without fighting others, you could get 75 SLP per day, it would be difficult to be perfect each day, but you could be good at some days and fight PVP as well and earn more. Solets assume the average for a newcomer is 75 SLP per day. How much is one SLP right now? $0.071 meaning 7 cents. If you earn 75 SLP per day that makes it 5.3 dollars per day.
If you do it for a full month, it makes around 160 bucks per month. Meaning you would need to do this for nearly 5 months to break even, and then you will also have the Axies. If the income drops, it takes longer, and SLP price keeps dropping constantly as well, even Axie prices are dropping. I would not say it is the worst investment, but it certainly doesn't look like the best neither.
I can still remember the time where SLP prices are its peak, you can get your initial investment in just 2 months like me.
I invested $1000 bucks on my first team on Axie and got it all in 2 months. Did I converted it into fiat? No but I bought another team instead with the same price.
Right now, 600$ investment on Axie will give you 3 "almost" worst axies IMO and with Ronin you don't need to pay fees since its free but it will just depend on how you will buy WETH that you will use to buy axies. For me, the lowest investment that one needs in order to have a decent team is at around 800$-900$.
Now with your computation, getting back your initial investment in 5 months isn't a best but comparing it to other investments I think that it is enough time to get your ROI. It isn't the best and it isn't the worst like you said. One thing to add too is that, there are many features that are coming to Axie in the upcoming months to years so if you want to make money in Axie then maybe try it. If you find it not a good investment for you then either sell your team or let your relative borrow it and you can get a passive income thru it as well. Like your computation though