I could write a book about "gamba bad", and we all know it's a disgusting, abhorrent practice, but I'll try to refrain from that and go against the proposed changes purely from gameplay perspective.
Gambling adds nothing to the game
At its core, this is a game about strategy, progression, and competition. The satisfaction comes from making smart decisions and watching steady progress over time.
Gambling isn't competitive in the sense it doesn't give other players a way to react - you could go big or go home all on your own. You could technically become wealthier than your own country in a matter of minutes.
Not to mention the inherent strategic gameplay has nothing to do with gambling.
It will drive players away
Since this game is completely f2p, there's no way to recover from big loses as easy as in say OSRS, where you just buy bonds/gold in a couple of seconds.
Since gambling is an endless loop of losing, no matter how "up" you are, you will end up with nothing in the end.
Every "win" reinforces the fact that you could either wait days or weeks for a couple of upgrades, or you could just get everything you want in a couple of minutes.
In the end, all the progress you have made, which might have taken you months, will be flushed down the drain in minutes, which brings me to my next point.
It encourages foul play
I've already mentioned how you can't buy in-game gold. Imagine you're a player who lost a months worth of progress in a couple of gambles, would you really want to stop now? The only way you can INSTANTLY generate gold is via gambling, so you break the rules: multiple accounts, vpns, proxies... Just for a chance to get back what you've had in the first place. Pretty non-sensical, right?
Following that, it may even be said that since gambling is a high risk endeavour, that it, without any other factors at play, makes regular players more likely to engage in risky behavior. Imagine watching your country go down because your president was too busy hitting the blackjack tables.
It shifts attention from the actual game
All the chats are going to be flooded with sore losers and lucky winners, screenshots of bad beats and big wins, discussions on rigged machines, RNG, RTP... I'm not saying war and gambling don't go together, that's not the point - soldiers gamble all the time, but the stakes are so high in this game, you might as well be gambling with your actual life.
Let me explain: When you gamble IRL, you usually don't bet your house, barracks, companies and mistress right away or ever! But in WarEra, just a couple of clicks gets you all of that on the table.
Economy, new players, culture
The impact on the game's economy cannot be overstated. Imagine what kind of turmoil it will cause: thousands if not tens of thousands pieces of gold being instantly added or removed from the game. As gambling activity grows, economic balance may become increasingly disconnected from the activities the game was designed to reward.
Also, as a new player, I don't see why I should wait for six months or more, with me being pretty disconnected from the game's actual virtues, when I can spin a couple of slots and get to the end game. This doesn't make any sense to me, nor would it go unnoticed by veteran players who've sacrificed so much to be where they are.
To conclude, if you want to gamble, stick with lootboxes or hit the casino IRL.