Really beautiful topic, dear friend! I always get emotional while discussing about this 😆. Let me explain my POV 😊.
I believe that God is devotee-lover. Bhaktavatsal. Generally devotees worship God in a specific form of their wish. May it be Purush form, or Prakriti form, or without form (Niraakar). That is called the own Ishta of that devotee. Devotee thinks about only that particular form of his Ishta whenever he thinks about God. So devotee-lover God understands his desire, & Bless him/communicate with him in that desired form. If children is happy, then parents also become happy, so God wants to make His devotee happy by providing his desired Ishta roop. There is no problem in loving one particular form of God as own Ishta, as it helps us to concentrate our mind on that desired roop. We can fix our focus on that roop which increases our devotion. And at the end of journey devotee wants to see his desired form & becomes one with that form.
But, problem arises when devotee starts to think that his Ishta is the best & all other forms are worst. He then forgets that the other forms are also His other forms Who is his Beloved! Being a Krishna devotee if one disrespects Shiv then he is obviously agyaani, ignorant, who does not know that Shiv is none but another form of Krishna only. If Krishna devotee disrespects Shiv then that disrespect will fall on Krishna Himself! This type of devotee can't be a true devotee, I think. True devotee receives this vision from Him so that he can understand that every form is His form only! There is nothing in this universe except God! When a soul ends own journey then can see that like it all other souls are ending their journeys & become one with God. And the fun is: there are many ways to reach God, & if you start walk in one of them, reach at the end, you will find that many other souls are reaching at the same place with you in spite of the case that their ways were different from yours! Then why should we devotees fight with each other when all of us are going to reach at the same point at the end of journey? Rather if we fight with others then it will divert us from the path, then why to take that risk? Whatever path we choose is completely okey until & unless we fall or divert from the path. So let's keep ourselves firm in our chosen paths, & pay respect to all devotees who are in different paths too. When you are meditating, if you get a vision of any Idol other than your Ishta, you must have to take that Idol as your Ishta only who have come in another form suddenly! If you can't think so then you are narrow minded who thinks that God has only one form which is my favorite, or God can't appear to others in any other form, only my Ishta is the true rests are false. But if you are a true devotee & believe that God is Almighty, then why is this limitation? Can the Sarva Shaktimaan not change own form? If you say no, then are not you thinking that His power is limited?
Sri Ramakrishna said: "The main intention is to climb on the roof (to reach the Ultimate). Now you may do this job by using the straight staircases, or by using a ladder, or by using a rope, even by using a bamboo. (The path is immaterial, keep your goal fixed) But whatever process you adopt, make sure that you will not fall at the midway! Do not dance while you are on the way to roof, if you dance you will fall (dancing = disturbing the devotion & knowledge)."
Also, He said, "If a mother has 5 sons with 5 different tastes, then the mother has to cook the same dish in 5 different ways to please all of them (same God has to take different forms to please different devotees)." But they can't fight with other as all of them are eating dish made by their mother only. Their mother knows which dish suits whom, so children must obey her decision. You are not His only child, right?
I live in Bengal. In Bengali culture, Divine Mother is most commonly worshipped as house deities & also as annual Durga Puja in autumn. We have bhajans of Divine Mother which says, "Don't know whether you are Purush or Prakriti, who can know it unless you Bless us with that realization? You took the form of half Radha & half Krishna in Vrindavan!" another one says, "Mother is Purush sometimes, Prakriti sometimes, & sometimes She becomes Niraakar!" also, "When you take the bow, we call you Ram, when you take the flute, we call you Krishna, when you take Trishul we call you Shiv & o Mother! When you take your sword we call you Kaali!" all song lines I quoted have the same indication.
One more thing I must add here. We do not know about our previous or next births. We might have worshipped God in different form in last birth, also may worship a different form in next one. Will that deviate us from our journey? No, never! But keeping this in mind, we should not disrespect other forms & devotees of those forms. I personally become overwhelmed while I think so! There is a song which expresses my emotion, "who knows in which names have I called you before! Who knows in which form I have made your Idol before! My endless journey towards you, that has not been started today!" I always tell everyone that, call Him with whatever Name you wish, but never stop to call Him! Love Him in whatever form you wish, but never stop to love Him!
And yes, the shloka you have quoted is known to me & it's one of my favorite shlokas! 😊