That's partly a good thing. You want all your potions and your best items on your strongest tower since a good amount of potions can double your tower's damage and a set of good items can also double it. Putting that on your strongest tower is the best choice.
You can give levels with level potions and unicorn tears.
If you put the starting tower in the middle or back, then your other towers can gain levels. I usually put my first tower in the middle and then fill the front area with scientist or towers with Painting of Solea.
Ow-men... i dont want to argue on what you like your strategies are Good to apply. its just You dont want to agree.. im so Sad. You dont like my idea.. of a little change about xp every wave. No offense This game is my favorite. Lets say I just got this problem for example. When one of my tower has a speed of 5k and dmg of 1b. Its anoying to see the other towers is just standing there lvl 17 while my first tower is lvl99 and over powering everything. This is just what i want to change.. too many Good strategies but i dont care i want change..! But i know they wont change it i just want to say all of these
If u played Bloons td6 they control lvl of the tower skill by purchasing lvls while earning coins on kill you dont get problems that it will became weakling even on the last tower you put.. or even on what no. waves you are in. all towers on the field are useful.. just pick any towers on the field you want to lvl so the towers on field is balance. You can make it also more powerful than your first tower you build. I already played this game the time that it has a infinite potion bug. I have super speed dmg crt. I didn't max out but i already seen its best. Thats how i notice these problems. & Dont report me. I already change my account to start fresh. 🙏😁.
Xp used to only be to the killing tower. Now it's based on damage, so if a tower does damage, then it gets xp.
I've had several games where I get most towers above 90, but the game doesn't give this to you for free.
The current ways to level up your towers: scientist, Solea, keys of wisdom, wolf pack, hologram
Would it be nice if the game gave all towers a little xp each wave? Maybe. I like the control over which towers receive xp. It isn't often, but sometimes it's useful to have a lower leveled tower. The only example that comes to mind is a gargoyle that you want to only knock back one square, not two.
Hmm, maybe Andy could make a new hero based on evenness. Force all towers to share xp and potions.
Edit:
See my card suggestion based on this idea
https://mazebert.com/forum/ideas/void-herald-hero--id1557/