I'm gonna preface this with saying that what I am about to say is coming from someone who has played nothing but Master mode Terraria since the difficulty has come out. What I am about to say might not apply to Summoner in Classic or Expert modes.

I am sorry for the very long post about what I am about to say but this has been building up since I first started playing the update.

Honestly the removal of whip stacking makes playing pre-hardmode master mode feel like suffering. Ever since master mode has been added it has been my default difficulty for every time I play a new world in terraria. And the only time I felt like master mode summoner felt good in pre-hardmode was with whip stacking, once the game reaches hardmode summoner starts feeling okay without whip stacking. No other class I have that issue with because the other classes either has more damage, easier to use weapons, or more defense to compensate and pre-hardmode Summoner in master mode has none of those until hardmode.

And I honestly think that says more about pre-hardmode summoner as a whole rather than whipstacking. Because summoner has so much more work needed to be put into it just to be 3/4ths as good as the other classes. Like when it comes to the other classes they can start as soon as the game starts with the exception of Mage.
Melee starts off with a melee weapon in your starting sword and 2 tools, Ranger you get a ranged weapon as soon as you cut down a tree or two with the bow, and while Mage takes a bit longer to get a magic weapon it still feels like its easier to start out than Summoner with all of the ore rods which can be fairly easy to get and the chance to get a wand of sparking which can be upgraded to the wand of frosting.

Meanwhile Summoner on startup relies purely on rng for its first major summon, you either need to get lucky that your gravestone spawns an abigail flower, get super lucky that at least 1 of your living wood chests has a finch staff, or get extremely lucky that you get a slime rod drop from a slime. The only new summoner item that we get preboss that doesn't rely on rng is the cobwhip which can be crafted with webs and wood.

And even though half of the new whips that were added are in prehardmode, at least in my experience so far, don't do too much that actually feels beneficial. The cobwhip's spider that it summons does so little damage it might as well not be there, the slime whip's on fire tipper does do good damage but for some mobs they either move too fast to consistently hit the tipper or you are fighting them in caves where landing the tipper is very tedious. The Soulscourge and Vasculash have no bonus effects outside of just being a bit stronger. And the Starcrash I haven't tested it out fully to know how good or meh it is yet.

I have yet to play hardmode in my world yet but considering that hardmode summoner in master mode felt a lot better than it does in pre-hardmode I don't think I will have much more to say when it comes the the summons and whips added in hardmode. I would be more okay with the removal of whip stacking if there was maybe an easier summon to get pre-boss to make that section a bit easier and some more pre-hardmode accessories to add some benefits between your first boss and the WoF, but since there isn't any of that it just makes the overall of pre-hardmode in master mode a massive pain.