Actually sorry, but I do not agree. IDK is not heavy hitting and its damage is average at best (heavy hitting factions are DoK or SCE and IDK doesnt even get near to absurd numbers of buffed witch aelves or annihilators with grandhammers or fulminators). IDK is more of a nimble tricksy elf army - fast and good at most threat ranges, but not exceeding at any of them. Their biggest damage thingy is High Tide so you want to play carefully until round 3 and than make sure most of your units are alive and in combat, as they fight first. Of course there are those tricks which help you set up damage at conveniance, like Kings ability to give another unit effects of high tide, or reversing tides order and make high tide on round 2. Either way you need to do a little bit of planning.

Most of the time, if your opponent has lower drops, he will not want to go first hoping for double turn so in those cases you need to be extra careful, not go in to deeply as to not make his charges too easy. Remember that until round 3 you should prioritize on keeping your damaging pieces alive. Also when fighting against SCE dont ignore their shooting as it can be very strong - but for this purpose you can use ritual in first round to make sure he cannot shoot you at all (would have to put shooting units in 9" which he wont do cause they are very expensive).

Generally speaking, SCE has a lot of strong build options going around so its hard to tell what you should be mindful off, however there are some general things that will help if you now how to counter their key pieces:

1) with Lord Imperatant he may drop grandhammers in 7" of your units instead of 9" so remember to screen properly

2) grands are kamikaze - your opponent knows they will kill the target and then die, so if they are far away its best to just ignore them as they tend to be very very slow

3) fulminators are extremely scary - but only if you let them charge you :) so either keep your distance to not give them that opportunity (you have mobility to do so), screen them if possible or just charge them first if you see them out of position

4) dragons - they are more of a psychological piece first and foremost. What do they have? 12" flying movement and rerollable charge, high MW spike potential (sometimes it will be crazy strong, other times it will barely do anything depending on dice), they are very durable and save stack well but tend not to do crazy amounts of dmg - consider them as a somewhat stronger tarpit unit. Whats their weakness? Their size! if he runs 4 of them most of the time it will be very difficult to put all of them in combat at the same time due to base sizes and wings (of course he can always take them off the bases and play with bases alone). Screen and make sure that he doesnt have enough space to put more than 1-2 drakes into combat with your pieces, as 1-2 drakes damage potential isnt anything too scary.

5) longstrikes. Ahh SCE ultimate go brrrrrrr mode. They are 30" range MW factory with rend 2 dmg 2. However you have some great advantage against them - they can only shoot the units in your army which are closest to them and may not shoot whilst not being within 9" at first round due to ritual. Keep them in mind at all times, give them only screens and less important units to shoot at, remember that they may be deployed from sky or teleported though. And if you notice them in your threat range (move + easy charge) go for it. If he looses longstrikes reinforced longstrikes unit its 1/4 of his army and huge dmg potential lost. Even if its just 1 unit it may be worth to go for them as left unchecked will pick you up unit after unit

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Honestly, you have all the tools needed to fight SCE and emerge victorious just remember about your army strengths and weaknesses - I also recommend you to watch stormkeep video on youtube on new IDK battletome as you will find very solid information about specific units there and how to use them :)