In Royal Revolt, two of the most common units are: Knights and Archers from level 1 to level 101 (so far), I use them all the time!
There is no reason Flare cannot allow the same boosts and additional levels of upgrades to make the Arrow Tower and Frost Tower usable from level 1 through level 100+.
Note: The Bomb Tower is useful all the way through!
Honestly, it’s just laziness/sloppiness. Instead of creating new (unnecessary) content like the Lighting Tower, why not make their existing content useful!
Obviously they tried to solve the imbalance with the Elite Boost: Poison Tower, and the War Boost for the Frost Tower: Frozen Spire.
But Poison Tower just isn’t enough! It should at the bare minimum provide the resistance to Fire that Tough Barricades provides.
And Frozen Spire is, of course, a total joke! If you are like me you use: Firestorm to Kill Frozen Spires and with the duration of Firestorm you’ll also kill the 3 silly Froster who spawn with the same Firestorm. (When I first saw Frozen Spires for the longest time I thought they weren’t function cause they and their Frosters were dying so quickly.)
Again being an early tower is no excuse for them being useless. As I said Knights and Archers are some of the most common units.
Plus notice the Arrow Tower is the only other Tower (aside from the Firebolt Tower) that actually fires a non-bomb projectile! They are really limiting the scope of the game-play.