The core inspiration was indeed vampire survivors and we decided to go with enough content which we knew we could complete in 3 days, hence no enemy variants.
The upgrades do work, I think it could have been better displayed with simple UI text displaying "purchased" but oh well. The dice was supposed to be purely random by applying a random force to any side and ignoring all other forces, however it ended up feeling "floaty".
The skip button was in a way to...well...skip the cards infront of you and continue back with the game. Maybe a cross button alongside would have been helpful but we ignore the need for one as it would have given the same function.
The game does get challenging on later waves with faster and stronger. For the encircling point, we did try spawning enemies right infront of you so that you would have to serve and turn to avoid enemies.
Alright so for your main concern, "Why create this?" firstly I think if we ask that question for every single thing we try making, humanity will end up nowhere. Putting the upgrades behind RNG was an interesting choice as it gave the player a much larger control over what upgrades they choose, should they spent the currency this round for an upgrade? Should they save the currency for later levels? Will the player roll a 1 or a 6 next turn, would they then be able to afford the upgrade they like? Would the upgrade they want even pop up? All these variables amounted to tons of replay ability and having people go for the "lucky" run where they would amass the most points. The current top leaderboard player told me they would pick +enemies spawn cards to achieve the highest possible score.
It comes down to personal preference where some people will choose guaranteed outcomes where logic, reasoning and planning, while others enjoy pure chaotic randomness.
You raised some valid points with OOB and dice issues, however I think you completely missed the mark on why we created this game.