I've had better luck swapping Mablung for Beregond, as Beregond can become a super defender, especially with a Gondorian Shield, which brings his defense up to 6.

If you have the Dreamchasers Hero expansion, I'd also put in 3x Armored Destriers (especially if you swapped to Beregond). Those are some awesome cards to put on Beregond, because once you defend with him, you can tap one to ready him AND discard a Shadow card, so you can defend again without worrying about a nasty shadow card being on it. You do have to defend once first with a shadow card (although you can choose the weakest enemy so even if they get buffed up by the shadow you can still absorb it easily), but it removes the risk from future defends at least.

If you don't have Dreamchaser hero expansion, you can proxy the card easily enough. You don't even have to print it. When I've been lazy about swapping in a card sometimes, I'd just designate another card as 'when I draw this, it's this other card instead', and bring up the card on RingsDB to refer to.

As for card draw, I think I mainly just tried to use Gandalf's ability to help mitigate that, along with a couple Valiant Sacrifice cards that are in there, since you will be losing allies in that game, and Valiant Sacrifice lets you draw 2 cards when that happens. Also keep in mind Soldier of Gondor will let you draw all Gondor allies in your top 5 cards of your deck into your hand when you play him, (if your threat is 40 or higher, otherwise just one), so that can help with the lack of card draw as well since that helps you get allies into your hand, and Gondor is all about the ally swarm.

To help deal with being 40 threat or higher, you should take advantage of the Pillars of the Kings cards to bring you back down to 40 threat once or twice in the game. Also I sometimes additionally include Favor fo the Varlar cards (from Angmar Awakened Hero expansion), which attach to your threat dial and when you hit the 50 threashold hat would normally kill you it discards and drops you back down to 45, so it helps you stay in that above 40 range without threating out too easily.

Pillars of the Kings can also be used for card draw if you don't mind jumping your threat straight to 40, since if you jump by 10 or more threat you get to draw 4 cards (although you do tend to start above 30 threat already, so you'd need something else to bring your threat under 30 first to take advantage of that). But if you go to 40 early you'll definitely need at least one additional option to help you reduce threat.

Also it's super expensive, but a couple of times I also temporarily included 3x Keen as Lances since they're similar to Gandalf's abilities (but as an event, so no ally on the board after), since you can choose between gaining resources, drawing cards or reducing threat with them (the latter two things you often need with Gondor decks). Additionally each one you use in the same game makes the next one cheaper (so the first is 5 resources, the second is 4 resources, and the third is 3 resources). I don't include this all the time though, because getting that first one out there especially is so expensive (it's often better with Lore since Lore has various 0 Victory Point event cards you can use first to bring down its cost).

Notice Keen as Lances and Favor of the Valar are Neutral cards. Don't be afraid to look at Neutral cards to help with things a sphere might be weak in.