Your strategy is cool, especially due to the fact that you didn't just select that high odd among them anyhow, but was on a good team. I didn't even expect a big odd for Barcelona against Deportivo Alavés that was on the 19th position in the relegation zone. Perhaps the bookie, based on experience, knew that Deportivo Alavés was desperate, and the fact that they were at home was another thing. I don't think Barcelona was even serious with that match, not minding how many tickets it would have ruined.
Now, I think 5-team parlay is even getting too risky for me, I would try to limit it to between 2 and 4, and see what's going to come out of it. I often lose mostly 1 of my leg parlays, and sometimes 2. The 2-for-5 parlay loss was so unusual.
This is me being naive like my team, looking at odds instead of thinking strategy, but then again Barca has a mentality that just says, we have to score! Don't remember the last time they ended a game without scoring

Now there's still a few games left... not going to bet on a team that's already a champion, qualifying for another European league they're more of a mediocre team without any effort, that could cost us more.
I'm still betting on them, this team tries to score goals even after 3-0, makes sense they still try to win after not needing to anymore.
I fell for it too, placed a bet on Barcelona against a bottom side odds that looked like easy money. Something felt off but I placed it anyway. They'd already won the league, nothing left to chase. Alaves meanwhile were desperate, literally playing to stay up. That's a dangerous spot to be betting against them.
I think with odds, and I thought they were still good enough to win, and they were chasing 100 points but yep, too soon after celebration lol