Oh I sense some buyer’s remorse here. I’m sorry that happened to you.
Read before you buy. Investigate the offers. Are they good enough for you? Do you understand them completely, including what you’re guaranteed to get and what you’re merely got a chance of getting? Do you understand the odds, as far as they’re published?
Invest your your for pleasurable things indeed. Consider your in-game purchase as money spent on entertainment. Consider your entertainment budget, and spend only what you’re willing to part with based on that budget. If you indeed think your purchase would be fun, for you. I nor @Morpheus can decide what’s enjoyable for you, that’s all your own personal prerogative.
Be aware that it’s very well possible to play this game for free. Things just take a whole lot longer that way. That’s not all bad, because this also spans the lifetime of the game for you. Remember training camps can drop 4 or even 5 star heroes if sufficiently upgraded, and ascension mats aren’t gated behind a paywall.
For me, I compare spending money on a game like this to buying a drink or a meal. You consume the drink/meal in an entertaining place, and all that’s left is the aftertaste and the filled stomach/quenched thirst. If that’s the height of your expectation, you’re less likely to experience buyer’s remorse.