Hi Diki
Don’t know where you have been for the last few years, but virtually all VSTi makers have either bought out completely new, or have adapted existing engines specifically for live on stage play. (The days of only being suitable for the studio are long gone)

Everyone:

Sound Balance:
Between individual VSTi, then yes there can be imbalances (Usually because they are designed by different sound teams) which is why all hosts give you individual control of each VSTi for volume, EQ, Reverb etc., and once setup (They are saved with the VST configuration) is not a problem.
Will they be as balanced as hardware arrangers?
Yes and No, as each person has their own idea of how they should be balanced, (Apart from the Korg, I find I have to alter the balances of a lot of the other OOTB hardware arrangers to get them anywhere near to what I want)

VSTi Arrangers:
Unfortunately with the demise of most of the high quality GM sound sets (Which dictate a specific balance) then style integration does become a touch more difficult. (Colossus was probably the highest quality with a quality that left the best sounds on hardware arrangers for dead (Fortunately it has been included with Goliath, but it is expensive)

Manufacture integration:
Your correct Wersi was continually working towards VSTi integration (Difficult with limited resources) as witnessed by B4 and VB3, which while you paid extra over the standalone instrument they did become one with the instrument, with no work needed by the user. (Hopefully Wersi will get themselves sorted and continue along these lines adding other VSTi)

Currently only 2 software based instruments are set up OOTB like Hardware boards and these are the Wersi Pegasus Wing keyboard and Apollo Organ. (A first for Wersi as they have never before in their entire 40 year history made an OOTB instrument, always believing that users who are prepared to spend this type of money would not be beginners, but those that want to do their own thing)

Is a software arranger for you?
There are plenty of free and trial software as well as reasonably priced soundcards and controllers out there, so you don’t need a large expenditure to try it out, but if you do go the pure software route then while there is a steep learning curve, it gives you a satisfaction (It’s all you and not somebody else’s work) that a hardware board just cannot provide IMO)

Me:
I have been using software based sound systems since the late 90s, and around 2003 moved over to Wersi OAS (Which got rid of all the cables and boxes, and allowed it into the lounge) and can categorically say that “for me”, there is no hardware board that comes anywhere close .

Is it for everybody?
No, so always try before committing yourself.

BFN

Bill